U.S. patent number 10,673,145 [Application Number 15/589,551] was granted by the patent office on 2020-06-02 for antenna system facilitating reduction of interfering signals.
This patent grant is currently assigned to Elwha LLC. The grantee listed for this patent is Elwha LLC. Invention is credited to Roderick A. Hyde, Jordin T. Kare, Lowell L. Wood, Jr..
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United States Patent |
10,673,145 |
Hyde , et al. |
June 2, 2020 |
Antenna system facilitating reduction of interfering signals
Abstract
Described embodiments include an antenna system and method. The
antenna system includes a surface scattering antenna that has an
electromagnetic waveguide structure and a plurality of
electromagnetic wave scattering elements. The plurality of
electromagnetic wave scattering elements are distributed along the
waveguide structure, have a respective activatable electromagnetic
response to a propagating electromagnetic wave, and produce a
controllable radiation pattern. A gain definition circuit defines a
radiation pattern configured to acquire a possible interfering
signal. The defined antenna radiation pattern has a field of view
covering at least a portion of an undesired field of view of an
associated antenna. An antenna controller establishes the defined
radiation pattern in the surface scattering antenna by activating
the respective electromagnetic response of selected electromagnetic
wave scattering elements. A correction circuit reduces an influence
of the received possible interfering signal in a contemporaneously
received signal by the associated antenna.
Inventors: |
Hyde; Roderick A. (Redmond,
WA), Kare; Jordin T. (San Jose, CA), Wood, Jr.; Lowell
L. (Bellevue, WA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Elwha LLC |
Bellevue |
WA |
US |
|
|
Assignee: |
Elwha LLC (Bellevue,
WA)
|
Family
ID: |
52825715 |
Appl.
No.: |
15/589,551 |
Filed: |
May 8, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170244172 A1 |
Aug 24, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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14058855 |
Oct 21, 2013 |
9647345 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01Q
15/0086 (20130101); H01Q 15/0053 (20130101); H01Q
1/28 (20130101); H01Q 13/20 (20130101); H01Q
3/443 (20130101) |
Current International
Class: |
H01Q
15/00 (20060101); H01Q 1/28 (20060101); H01Q
13/20 (20060101); H01Q 3/44 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2007-081825 |
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Mar 2007 |
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JP |
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2008-054146 |
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Mar 2008 |
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JP |
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2010-187141 |
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Aug 2010 |
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JP |
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10-1045585 |
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Jun 2011 |
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KR |
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WO-2008/007545 |
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Jan 2008 |
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WO |
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WO-2008/059292 |
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May 2008 |
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WO |
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WO-2009/103042 |
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Aug 2009 |
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WO |
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WO-2010/021736 |
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Feb 2010 |
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WO |
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WO-2013/147470 |
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Oct 2013 |
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WO |
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|
Primary Examiner: Tran; Hai V
Assistant Examiner: Bouizza; Michael M
Attorney, Agent or Firm: Foley & Lardner LLP
Parent Case Text
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
The present application is a continuation of U.S. patent
application Ser. No. 14/058,855, filed Oct. 21, 2013, which is
incorporated herein by reference in its entirety and for all
purposes.
Claims
What is claimed is:
1. An antenna system comprising: a surface scattering antenna
including: an electromagnetic waveguide structure; a plurality of
electromagnetic wave scattering elements distributed along the
waveguide structure and operable in combination to produce a
controllable radiation pattern; a gain definition circuit
configured to define a radiation pattern configured to receive a
possible interfering signal transmitted within an operating
frequency band of an associated antenna, the associated antenna
having a field of view that includes a desired field of view and an
undesired field of view, and the defined antenna radiation pattern
having a field of view covering at least a portion of the undesired
field of view of the associated antenna, wherein the undesired
field of view includes the possible interfering signal, and the
desired field of view includes a target signal; and a correction
circuit configured to reduce an influence of the received possible
interfering signal in a contemporaneously received signal by the
associated antenna.
2. The system of claim 1, further comprising an antenna controller
configured to establish the defined radiation pattern in the
surface scattering antenna by activating a respective
electromagnetic response of selected electromagnetic wave
scattering elements of the plurality of electromagnetic wave
scattering elements.
3. The system of claim 1, wherein the aperture of the surface
scattering antenna is less than 50% of the aperture of the
associated antenna.
4. The system of claim 1, wherein the plurality of electromagnetic
wave scattering elements have an inter-element spacing
substantially less than a free-space wavelength of a highest
operating frequency of the surface scattering antenna, and each
electromagnetic wave scattering element of the plurality of
electromagnetic wave scattering elements has a respective
activatable electromagnetic response to a guided wave propagating
in the waveguide structure.
5. The system of claim 1, wherein the surface scattering antenna
includes a planar or non-planar surface scattering element.
6. The system of claim 1, wherein the plurality of electromagnetic
wave scattering elements are operable in combination to produce a
controllable radiation envelope.
7. The system of claim 1, wherein the plurality of electromagnetic
wave scattering elements are operable in combination to produce a
controllable radiation pattern in response to a control signal.
8. The system of claim 1, wherein the defined radiation pattern is
selected based on trial and error.
9. The system of claim 1, wherein the defined radiation pattern is
selected from a library of potential radiation patterns.
10. The system of claim 1, wherein the defined radiation pattern is
selected from a history of radiation patterns previously
established in the surface scattering antenna.
11. The system of claim 1, wherein the desired field of view of the
associated antenna includes a skyward or hemispherical view.
12. The system of claim 1, wherein the antenna controller is
configured to establish the defined radiation pattern in the
surface scattering antenna by applying a bias activating the
respective electromagnetic response of the electromagnetic wave
scattering elements of the plurality of electromagnetic wave
scattering elements.
13. The system of claim 12, wherein the bias includes a bias
voltage, bias field, bias current, or biasing mechanical
inputs.
14. The system of claim 1, wherein the possible interfering signal
includes a possible jamming signal.
15. The system of claim 1, wherein the possible interfering signal
includes a possible spoofing signal.
16. The system of claim 1, wherein the possible interfering signal
includes a possible malicious signal.
17. The system of claim 1, wherein the possible interfering signal
includes a possible intentionally interfering signal.
18. The system of claim 17, wherein the adaptive correction circuit
includes use of space-time adaptive processing in reducing an
influence of the received possible interfering signal in the
contemporaneously received signal.
19. The system of claim 1, wherein the possible interfering signal
includes a possible unintentionally interfering signal.
20. The system of claim 1, wherein the correction circuit includes
an adaptive correction circuit.
21. The system of claim 20, wherein the adaptive correction circuit
is configured to determine phase and amplitudes of the received
possible interfering signal and the contemporaneously received
signal, and to combine the possible interfering signal and the
contemporaneously received signal to produce a reduction of an
influence of the received possible interfering signal in the
contemporaneously received signal.
22. The system of claim 1, wherein a peripheral portion of the
associated antenna includes the surface scattering antenna.
23. The system of claim 22, wherein the peripheral portion of the
associated antenna includes an electromagnetic wave deflecting
structure configured to direct an arriving electromagnetic wave
into the defined radiation pattern on the surface scattering
antenna.
24. The system of claim 23, wherein the wave deflecting structure
includes a wave reflecting structure.
25. The system of claim 23, wherein the wave deflecting structure
includes a lens structure.
26. The system of claim 23, wherein the wave deflecting structure
includes a prism structure.
27. The system of claim 1, wherein the surface scattering antenna
is configured to be mounted on an airborne vehicle.
28. The system of claim 1, wherein the surface scattering antenna
is configured to be mounted on a missile.
29. The system of claim 1, wherein the surface scattering antenna
is configured to be mounted on a terrestrial vehicle.
30. An antenna system comprising: a surface scattering antenna
including: an electromagnetic waveguide structure; a plurality of
electromagnetic wave scattering elements distributed along the
waveguide structure and operable in combination to produce a
controllable radiation pattern; a gain definition circuit
configured to define a radiation pattern configured to receive a
possible interfering signal transmitted within an operating
frequency band of an associated antenna, the associated antenna
having a field of view that includes a desired field of view and an
undesired field of view, and the defined antenna radiation pattern
having a field of view covering at least a portion of the undesired
field of view of the associated antenna, wherein the undesired
field of view includes the possible interfering signal, and the
desired field of view includes a target signal.
31. The system of claim 30, further comprising a correction circuit
configured to reduce an influence of the received possible
interfering signal in a contemporaneously received signal by the
associated antenna.
32. The system of claim 30, further comprising an antenna
controller configured to establish the defined radiation pattern in
the surface scattering antenna by activating a respective
electromagnetic response of selected electromagnetic wave
scattering elements of the plurality of electromagnetic wave
scattering elements.
33. An antenna system comprising: a surface scattering antenna
including: an electromagnetic waveguide structure; a plurality of
electromagnetic wave scattering elements distributed along the
waveguide structure and operable in combination to produce a
controllable radiation pattern, wherein the plurality of
electromagnetic wave scattering elements have an inter-element
spacing substantially less than a free-space wavelength of a
highest operating frequency of the surface scattering antenna, and
each electromagnetic wave scattering element of the plurality of
electromagnetic wave scattering elements has a respective
activatable electromagnetic response to a guided wave propagating
in the waveguide structure; and a gain definition circuit
configured to define a radiation pattern configured to receive a
possible interfering signal transmitted within an operating
frequency band of an associated antenna, the associated antenna
having a field of view that includes a desired field of view and an
undesired field of view, and the defined antenna radiation pattern
having a field of view covering at least a portion of the undesired
field of view of the associated antenna, wherein the undesired
field of view includes the possible interfering signal, and the
desired field of view includes a target signal.
Description
If an Application Data Sheet (ADS) has been filed on the filing
date of this application, it is incorporated by reference herein.
Any applications claimed on the ADS for priority under 35 U.S.C.
.sctn..sctn. 119, 120, 121, or 365(c), and any and all parent,
grandparent, great-grandparent, etc. applications of such
applications, are also incorporated by reference, including any
priority claims made in those applications and any material
incorporated by reference, to the extent such subject matter is not
inconsistent herewith.
SUBJECT-MATTER-RELATED APPLICATIONS
U.S. Patent Application No. 61/455,171, entitled SURFACE SCATTERING
ANTENNAS, naming NATHAN KUNDTZ ET AL. as inventors, filed Oct. 15,
2010, is related to the present application.
U.S. patent application Ser. No. 13/317,338, entitled SURFACE
SCATTERING ANTENNAS, naming ADAM BILY, ANNA K. BOARDMAN, RUSSELL J.
HANNIGAN, JOHN HUNT, NATHAN KUNDTZ, DAVID R. NASH, RYAN ALLAN
STEVENSON, AND PHILIP A. SULLIVAN, as inventors, filed Oct. 14,
2011, is related to the present application.
U.S. patent application Ser. No. 13/838,934, entitled SURFACE
SCATTERING ANTENNA IMPROVEMENTS, naming ADAM BILY, JEFF DALLAS,
RUSSELL HANNIGAN, NATHAN KUNDTZ, DAVID R. NASH, and RYAN ALLAN
STEVENSON as inventors, filed Mar. 15, 2013, is related to the
present application.
If the listings of applications provided above are inconsistent
with the listings provided via an ADS, it is the intent of the
Applicant to claim priority to each application that appears in the
Priority Applications section of the ADS and to each application
that appears in Priority Applications section of this
application.
All subject matter of the Priority Applications and the Related
Applications and of any and all parent, grandparent,
great-grandparent, etc. applicants of the Priority Applications and
the Related Applications, including any priority claims, is
incorporated herein by reference to the extent such subject matter
is not inconsistent herewith. All subject matter of these Related
Applications is incorporated herein by reference to the extent such
subject matter is not inconsistent herewith.
SUMMARY OF THE INVENTION
For example, and without limitation, an embodiment of the subject
matter described herein includes an antenna system. The antenna
system includes a surface scattering antenna. The surface
scattering antenna includes an electromagnetic waveguide structure
and a plurality of electromagnetic wave scattering elements. The
plurality of electromagnetic wave scattering elements are
distributed along the waveguide structure and have an inter-element
spacing substantially less than a free-space wavelength of a
highest operating frequency of the surface scattering antenna. Each
electromagnetic wave scattering element of the plurality of
electromagnetic wave scattering elements has a respective
activatable electromagnetic response to a guided wave propagating
in the waveguide structure. The plurality of electromagnetic wave
scattering elements are operable in combination to produce a
controllable radiation pattern. The antenna system includes a gain
definition circuit configured to define a radiation pattern
configured to receive a possible interfering signal transmitted
within an operating frequency band of an associated antenna having
field of view that includes a desired field of view and an
undesired field of view. The defined antenna radiation pattern
having a field of view covering at least a portion of the undesired
field of view of the associated antenna. The antenna system
includes an antenna controller configured to establish the defined
radiation pattern in the surface scattering antenna by activating
the respective electromagnetic response of selected electromagnetic
wave scattering elements of the plurality of electromagnetic wave
scattering elements. The antenna system includes a correction
circuit configured to reduce an influence of the received possible
interfering signal in a contemporaneously received signal by the
associated antenna.
In an embodiment, the antenna system includes the associated
antenna with the desired field of view. In an embodiment, the
antenna system includes a space-based navigation system
receiver.
For example, and without limitation, an embodiment of the subject
matter described herein includes a method. The method includes
defining an antenna radiation pattern configured to receive in a
surface scattering antenna a possible interfering signal
transmitted within an operating frequency band of an associated
antenna. The associated antenna having field of view that includes
a desired field of view and an undesired field of view, and the
surface scattering antenna having a field of view covering at least
a portion of the undesired field of view. The method includes
establishing the defined radiation pattern in the surface
scattering antenna by respectively activating the electromagnetic
response of selected electromagnetic wave scattering elements of
the plurality of electromagnetic wave scattering elements. The
method includes receiving the possible interfering signal with the
defined antenna radiation pattern established in the surface
scattering antenna. The method includes reducing an influence of
the possible interfering signal in a contemporaneously received
signal by the associated antenna. The surface scattering antenna
includes an electromagnetic waveguide structure, and the plurality
of electromagnetic wave scattering elements. The plurality of
electromagnetic wave scattering elements are distributed along the
waveguide structure and having an inter-element spacing
substantially less than a free-space wavelength of a highest
operating frequency of the surface scattering antenna. Each
electromagnetic wave scattering element of the plurality of
electromagnetic wave scattering elements has a respective
activatable electromagnetic response to a guided wave propagating
in the waveguide structure. The plurality of electromagnetic wave
scattering elements are operable in combination to produce a
controllable radiation pattern.
In an embodiment, the method includes reshaping the antenna
radiation pattern established in the surface scattering antenna in
response to an aspect of the received possible interfering signal.
In this embodiment, the method also includes receiving another
instance of the possible interfering signal on the operating
frequency of the another antenna with the dynamically reshaped
antenna radiation pattern established in the surface scattering
antenna. In this embodiment, the reducing includes reducing an
influence of the possible interfering signal in a contemporaneously
received signal by the associated antenna based upon the received
another instance of the possible interfering signal.
For example, and without limitation, an embodiment of the subject
matter described herein includes an antenna system. The antenna
system includes means for defining an antenna radiation pattern
configured to receive in a surface scattering antenna a possible
interfering signal transmitted within an operating frequency band
of an associated antenna. The associated antenna has field of view
that includes a desired field of view and an undesired field of
view, and the surface scattering antenna has a field of view
covering at least a portion of the undesired field of view. The
antenna system includes means for establishing the defined
radiation pattern in the surface scattering antenna by respectively
activating the electromagnetic response of selected electromagnetic
wave scattering elements of the plurality of electromagnetic wave
scattering elements. The antenna system includes means for
receiving the possible interfering signal with the defined antenna
radiation pattern established in the surface scattering antenna.
The antenna system includes means for reducing an influence of the
possible interfering signal in a signal contemporaneously received
by the associated antenna. The surface scattering antenna includes
an electromagnetic waveguide structure, and the plurality of
electromagnetic wave scattering elements. The plurality of
electromagnetic wave scattering elements are distributed along the
waveguide structure and having an inter-element spacing
substantially less than a free-space wavelength of a highest
operating frequency of the surface scattering antenna. Each
electromagnetic wave scattering element of the plurality of
electromagnetic wave scattering elements has a respective
activatable electromagnetic response to a guided wave propagating
in the waveguide structure. The plurality of electromagnetic wave
scattering elements are operable in combination to produce a
controllable radiation pattern.
The foregoing summary is illustrative only and is not intended to
be in any way limiting. In addition to the illustrative aspects,
embodiments, and features described above, further aspects,
embodiments, and features will become apparent by reference to the
drawings and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic depiction of a surface scattering
antenna.
FIGS. 2A and 2B respectively depict an exemplary adjustment pattern
and corresponding beam pattern for a surface scattering
antenna.
FIGS. 3A and 3B respectively depict another exemplary adjustment
pattern and corresponding beam pattern for a surface scattering
antenna.
FIGS. 4A and 4B respectively depict another exemplary adjustment
pattern and corresponding field pattern for a surface scattering
antenna.
FIG. 5 depicts an embodiment of a surface scattering antenna
including a patch element.
FIGS. 6A and 6B depict examples of patch elements on a
waveguide.
FIG. 6C depicts field lines for a waveguide mode.
FIG. 7 depicts a liquid crystal arrangement.
FIGS. 8A and 8B depict exemplary counter-electrode
arrangements.
FIG. 9 depicts a surface scattering antenna with direct addressing
of the scattering elements.
FIG. 10 depicts a surface scattering antenna with matrix addressing
of the scattering elements.
FIGS. 11A, 12A, and 13 depict various bias voltage drive
schemes.
FIGS. 11B and 12B depict bias voltage drive circuitry.
FIG. 14 depicts a system block diagram.
FIGS. 15 and 16 depict flow diagrams.
FIG. 17 illustrates an example embodiment of an environment 1719
that includes a thin computing device 1720 in which embodiments may
be implemented;
FIG. 18 illustrates an example embodiment of an environment 1800
that includes a general-purpose computing system 1810 in which
embodiments may be implemented;
FIG. 19 illustrates an environment 1900 in which embodiments may be
implemented;
FIG. 20 schematically illustrates components 1920 of the antenna
system 1905;
FIG. 21 schematically illustrates fields of view of the surface
scattering antenna 1910 and the associated antenna 1980;
FIG. 22 illustrates an example operational flow 2000;
FIG. 23 illustrates an example system 2100;
FIG. 24 illustrates an environment 2300 in which embodiments may be
implemented;
FIG. 25 illustrates the components 2350 of the antenna system
2305;
FIG. 26 illustrates an example operational flow 2400; and
FIG. 27 illustrates an example system 2500.
DETAILED DESCRIPTION
In the following detailed description, reference is made to the
accompanying drawings, which form a part hereof. In the drawings,
similar symbols typically identify similar components, unless
context dictates otherwise. The illustrative embodiments described
in the detailed description, drawings, and claims are not meant to
be limiting. Other embodiments may be utilized, and other changes
may be made, without departing from the spirit or scope of the
subject matter presented here.
A schematic illustration of a surface scattering antenna is
depicted in FIG. 1. The surface scattering antenna 100 includes a
plurality of scattering elements 102a, 102b that are distributed
along a wave-propagating structure 104. The wave propagating
structure 104 may be a microstrip, a coplanar waveguide, a parallel
plate waveguide, a dielectric slab, a closed or tubular waveguide,
or any other structure capable of supporting the propagation of a
guided wave or surface wave 105 along or within the structure. The
wave-propagation structure may be an energy feeding structure. The
wavy line 105 is a symbolic depiction of the guided wave or surface
wave, and this symbolic depiction is not intended to indicate an
actual wavelength or amplitude of the guided wave or surface wave;
moreover, while the wavy line 105 is depicted as within the
wave-propagating structure 104 (e.g. as for a guided wave in a
metallic waveguide), for a surface wave the wave may be
substantially localized outside the wave-propagating structure
(e.g. as for a TM mode on a single wire transmission line or a
"spoof plasmon" on an artificial impedance surface). The scattering
elements 102a, 102b may include scattering elements that are
embedded within, positioned on a surface of, or positioned within
an evanescent proximity of, the wave-propagation structure 104. For
example, the scattering elements can include complementary
metamaterial elements such as those presented in D. R. Smith et al,
"Metamaterials for surfaces and waveguides," U.S. Patent
Application Publication No. 2010/0156573, and A. Bily et al,
"Surface scattering antennas," U.S. Patent Application Publication
No. 2012/0194399, each of which is herein incorporated by
reference. As another example, the scattering elements can include
patch elements, as discussed below.
The surface scattering antenna also includes at least one feed
connector 106 that is configured to couple the wave-propagation
structure 104 to a feed structure 108. The feed structure 108
(schematically depicted as a coaxial cable) may be a transmission
line, a waveguide, or any other structure capable of providing an
electromagnetic signal that may be launched, via the feed connector
106, into a guided wave or surface wave 105 of the wave-propagating
structure 104. The feed connector 106 may be, for example, a
coaxial-to-microstrip connector (e.g. an SMA-to-PCB adapter), a
coaxial-to-waveguide connector, a mode-matched transition section,
etc. While FIG. 1 depicts the feed connector in an "end-launch"
configuration, whereby the guided wave or surface wave 105 may be
launched from a peripheral region of the wave-propagating structure
(e.g. from an end of a microstrip or from an edge of a parallel
plate waveguide), in other embodiments the feed structure may be
attached to a non-peripheral portion of the wave-propagating
structure, whereby the guided wave or surface wave 105 may be
launched from that non-peripheral portion of the wave-propagating
structure (e.g. from a midpoint of a microstrip or through a hole
drilled in a top or bottom plate of a parallel plate waveguide);
and yet other embodiments may provide a plurality of feed
connectors attached to the wave-propagating structure at a
plurality of locations (peripheral and/or non-peripheral).
The scattering elements 102a, 102b are adjustable scattering
elements having electromagnetic properties that are adjustable in
response to one or more external inputs. Various embodiments of
adjustable scattering elements are described, for example, in D. R.
Smith et al, previously cited, and further in this disclosure.
Adjustable scattering elements can include elements that are
adjustable in response to voltage inputs (e.g. bias voltages for
active elements (such as varactors, transistors, diodes) or for
elements that incorporate tunable dielectric materials (such as
ferroelectrics or liquid crystals)), current inputs (e.g. direct
injection of charge carriers into active elements), optical inputs
(e.g. illumination of a photoactive material), field inputs (e.g.
magnetic fields for elements that include nonlinear magnetic
materials), mechanical inputs (e.g. MEMS, actuators, hydraulics),
etc. In the schematic example of FIG. 1, scattering elements that
have been adjusted to a first state having first electromagnetic
properties are depicted as the first elements 102a, while
scattering elements that have been adjusted to a second state
having second electromagnetic properties are depicted as the second
elements 102b. The depiction of scattering elements having first
and second states corresponding to first and second electromagnetic
properties is not intended to be limiting: embodiments may provide
scattering elements that are discretely adjustable to select from a
discrete plurality of states corresponding to a discrete plurality
of different electromagnetic properties, or continuously adjustable
to select from a continuum of states corresponding to a continuum
of different electromagnetic properties. Moreover, the particular
pattern of adjustment that is depicted in FIG. 1 (i.e. the
alternating arrangement of elements 102a and 102b) is only an
exemplary configuration and is not intended to be limiting.
In the example of FIG. 1, the scattering elements 102a, 102b have
first and second couplings to the guided wave or surface wave 105
that are functions of the first and second electromagnetic
properties, respectively. For example, the first and second
couplings may be first and second polarizabilities of the
scattering elements at the frequency or frequency band of the
guided wave or surface wave. In one approach the first coupling is
a substantially nonzero coupling whereas the second coupling is a
substantially zero coupling. In another approach both couplings are
substantially nonzero but the first coupling is substantially
greater than (or less than) than the second coupling. On account of
the first and second couplings, the first and second scattering
elements 102a, 102b are responsive to the guided wave or surface
wave 105 to produce a plurality of scattered electromagnetic waves
having amplitudes that are functions of (e.g. are proportional to)
the respective first and second couplings. A superposition of the
scattered electromagnetic waves comprises an electromagnetic wave
that is depicted, in this example, as a plane wave 110 that
radiates from the surface scattering antenna 100.
The emergence of the plane wave may be understood by regarding the
particular pattern of adjustment of the scattering elements (e.g.
an alternating arrangement of the first and second scattering
elements in FIG. 1) as a pattern that defines a grating that
scatters the guided wave or surface wave 105 to produce the plane
wave 110. Because this pattern is adjustable, some embodiments of
the surface scattering antenna may provide adjustable gratings or,
more generally, holograms, where the pattern of adjustment of the
scattering elements may be selected according to principles of
holography. Suppose, for example, that the guided wave or surface
wave may be represented by a complex scalar input wave .PSI..sub.in
that is a function of position along the wave-propagating structure
104, and it is desired that the surface scattering antenna produce
an output wave that may be represented by another complex scalar
wave .PSI..sub.out. Then a pattern of adjustment of the scattering
elements may be selected that corresponds to an interference
pattern of the input and output waves along the wave-propagating
structure. For example, the scattering elements may be adjusted to
provide couplings to the guided wave or surface wave that are
functions of (e.g. are proportional to, or step-functions of) an
interference term given by Re[.PSI..sub.out .PSI.*.sub.in]. In this
way, embodiments of the surface scattering antenna may be adjusted
to provide arbitrary antenna radiation patterns by identifying an
output wave .PSI..sub.out corresponding to a selected beam pattern,
and then adjusting the scattering elements accordingly as above.
Embodiments of the surface scattering antenna may therefore be
adjusted to provide, for example, a selected beam direction (e.g.
beam steering), a selected beam width or shape (e.g. a fan or
pencil beam having a broad or narrow beamwidth), a selected
arrangement of nulls (e.g. null steering), a selected arrangement
of multiple beams, a selected polarization state (e.g. linear,
circular, or elliptical polarization), a selected overall phase, or
any combination thereof. Alternatively or additionally, embodiments
of the surface scattering antenna may be adjusted to provide a
selected near field radiation profile, e.g. to provide near-field
focusing and/or near-field nulls.
Because the spatial resolution of the interference pattern is
limited by the spatial resolution of the scattering elements, the
scattering elements may be arranged along the wave-propagating
structure with inter-element spacings that are much less than a
free-space wavelength corresponding to a highest operating
frequency of the device (for example, less than one-third,
one-fourth, or one-fifth of this free-space wavelength). In some
approaches, the operating frequency is a microwave frequency,
selected from frequency bands such as L, S, C, X, Ku, K, Ka, Q, U,
V, E, W, F, and D, corresponding to frequencies ranging from about
1 GHz to 170 GHz and free-space wavelengths ranging from
millimeters to tens of centimeters. In other approaches, the
operating frequency is an RF frequency, for example in the range of
about 100 MHz to 1 GHz. In yet other approaches, the operating
frequency is a millimeter-wave frequency, for example in the range
of about 170 GHz to 300 GHz. These ranges of length scales admit
the fabrication of scattering elements using conventional printed
circuit board or lithographic technologies.
In some approaches, the surface scattering antenna includes a
substantially one-dimensional wave-propagating structure 104 having
a substantially one-dimensional arrangement of scattering elements,
and the pattern of adjustment of this one-dimensional arrangement
may provide, for example, a selected antenna radiation profile as a
function of zenith angle (i.e. relative to a zenith direction that
is parallel to the one-dimensional wave-propagating structure). In
other approaches, the surface scattering antenna includes a
substantially two-dimensional wave-propagating structure 104 having
a substantially two-dimensional arrangement of scattering elements,
and the pattern of adjustment of this two-dimensional arrangement
may provide, for example, a selected antenna radiation profile as a
function of both zenith and azimuth angles (i.e. relative to a
zenith direction that is perpendicular to the two-dimensional
wave-propagating structure). Exemplary adjustment patterns and beam
patterns for a surface scattering antenna that includes a
two-dimensional array of scattering elements distributed on a
planar rectangular wave-propagating structure are depicted in FIGS.
2A-4B. In these exemplary embodiments, the planar rectangular
wave-propagating structure includes a monopole antenna feed that is
positioned at the geometric center of the structure. FIG. 2A
presents an adjustment pattern that corresponds to a narrow beam
having a selected zenith and azimuth as depicted by the beam
pattern diagram of FIG. 2B. FIG. 3A presents an adjustment pattern
that corresponds to a dual-beam far field pattern as depicted by
the beam pattern diagram of FIG. 3B. FIG. 4A presents an adjustment
pattern that provides near-field focusing as depicted by the field
intensity map of FIG. 4B (which depicts the field intensity along a
plane perpendicular to and bisecting the long dimension of the
rectangular wave-propagating structure).
In some approaches, the wave-propagating structure is a modular
wave-propagating structure and a plurality of modular
wave-propagating structures may be assembled to compose a modular
surface scattering antenna. For example, a plurality of
substantially one-dimensional wave-propagating structures may be
arranged, for example, in an interdigital fashion to produce an
effective two-dimensional arrangement of scattering elements. The
interdigital arrangement may comprise, for example, a series of
adjacent linear structures (i.e. a set of parallel straight lines)
or a series of adjacent curved structures (i.e. a set of
successively offset curves such as sinusoids) that substantially
fills a two-dimensional surface area. These interdigital
arrangements may include a feed connector having a tree structure,
e.g. a binary tree providing repeated forks that distribute energy
from the feed structure 108 to the plurality of linear structures
(or the reverse thereof). As another example, a plurality of
substantially two-dimensional wave-propagating structures (each of
which may itself comprise a series of one-dimensional structures,
as above) may be assembled to produce a larger aperture having a
larger number of scattering elements; and/or the plurality of
substantially two-dimensional wave-propagating structures may be
assembled as a three-dimensional structure (e.g. forming an A-frame
structure, a pyramidal structure, or other multi-faceted
structure). In these modular assemblies, each of the plurality of
modular wave-propagating structures may have its own feed
connector(s) 106, and/or the modular wave-propagating structures
may be configured to couple a guided wave or surface wave of a
first modular wave-propagating structure into a guided wave or
surface wave of a second modular wave-propagating structure by
virtue of a connection between the two structures.
In some applications of the modular approach, the number of modules
to be assembled may be selected to achieve an aperture size
providing a desired telecommunications data capacity and/or quality
of service, and/or a three-dimensional arrangement of the modules
may be selected to reduce potential scan loss. Thus, for example,
the modular assembly could comprise several modules mounted at
various locations/orientations flush to the surface of a vehicle
such as an aircraft, spacecraft, watercraft, ground vehicle, etc.
(the modules need not be contiguous). In these and other
approaches, the wave-propagating structure may have a substantially
non-linear or substantially non-planar shape whereby to conform to
a particular geometry, therefore providing a conformal surface
scattering antenna (conforming, for example, to the curved surface
of a vehicle).
More generally, a surface scattering antenna is a reconfigurable
antenna that may be reconfigured by selecting a pattern of
adjustment of the scattering elements so that a corresponding
scattering of the guided wave or surface wave produces a desired
output wave. Suppose, for example, that the surface scattering
antenna includes a plurality of scattering elements distributed at
positions {r.sub.j} along a wave-propagating structure 104 as in
FIG. 1 (or along multiple wave-propagating structures, for a
modular embodiment) and having a respective plurality of adjustable
couplings {.alpha..sub.j} to the guided wave or surface wave 105.
The guided wave or surface wave 105, as it propagates along or
within the (one or more) wave-propagating structure(s), presents a
wave amplitude A.sub.j and phase .phi..sub.j to the jth scattering
element; subsequently, an output wave is generated as a
superposition of waves scattered from the plurality of scattering
elements:
E(.theta.,.PHI.)=.SIGMA..sub.jR.sub.j(.theta.,.PHI.).alpha..sub.jA.sub.je-
.sup.i.phi..sup.je.sup.i(k(.theta.,.PHI.)r.sup.j.sup.), (1)
where E(.theta.,.phi.) represents the electric field component of
the output wave on a far-field radiation sphere,
R.sub.j(.theta.,.phi.) represents a (normalized) electric field
pattern for the scattered wave that is generated by the jth
scattering element in response to an excitation caused by the
coupling .alpha..sub.j, and k(.theta.,.phi.) represents a wave
vector of magnitude .omega./c that is perpendicular to the
radiation sphere at (.theta.,.phi.). Thus, embodiments of the
surface scattering antenna may provide a reconfigurable antenna
that is adjustable to produce a desired output wave
E(.theta.,.phi.) by adjusting the plurality of couplings
{.alpha..sub.j} in accordance with equation (1).
The wave amplitude A.sub.j and phase .phi..sub.j of the guided wave
or surface wave are functions of the propagation characteristics of
the wave-propagating structure 104. These propagation
characteristics may include, for example, an effective refractive
index and/or an effective wave impedance, and these effective
electromagnetic properties may be at least partially determined by
the arrangement and adjustment of the scattering elements along the
wave-propagating structure. In other words, the wave-propagating
structure, in combination with the adjustable scattering elements,
may provide an adjustable effective medium for propagation of the
guided wave or surface wave, e.g. as described in D. R. Smith et
al, previously cited. Therefore, although the wave amplitude
A.sub.j and phase .phi..sub.j of the guided wave or surface wave
may depend upon the adjustable scattering element couplings
{.alpha..sub.j} (i.e. A.sub.i=A.sub.i({.alpha..sub.j}),
.phi..sub.j=.phi..sub.j({.alpha..sub.j})), in some embodiments
these dependencies may be substantially predicted according to an
effective medium description of the wave-propagating structure.
In some approaches, the reconfigurable antenna is adjustable to
provide a desired polarization state of the output wave
E(.theta.,.phi.). Suppose, for example, that first and second
subsets LP.sup.(1) and LP.sup.(2) of the scattering elements
provide (normalized) electric field patterns
R.sup.(1)(.theta.,.phi.) and R.sup.(2) (.theta.,.phi.),
respectively, that are substantially linearly polarized and
substantially orthogonal (for example, the first and second
subjects may be scattering elements that are perpendicularly
oriented on a surface of the wave-propagating structure 104). Then
the antenna output wave E(.theta.,.phi.) may be expressed as a sum
of two linearly polarized components:
E(.theta.,.PHI.)=E.sup.(1)(.theta.,.PHI.)+E.sup.(2)(.theta.,.PHI.)=.LAMBD-
A..sup.(1)R.sup.(1)(.theta.,.PHI.)+.LAMBDA..sup.(2)R.sup.(2)(.theta.,.PHI.-
) (2)
where .LAMBDA..sup.(1,2)(.theta.,.PHI.)=.SIGMA..sub.j
LP.sub.(1,2).alpha..sub.jA.sub.je.sup.i.phi..sup.je.sup.i(k)(.theta.,.PHI-
.)r.sup.j.sup.) (3)
are the complex amplitudes of the two linearly polarized
components. Accordingly, the polarization of the output wave
E(.theta.,.phi.) may be controlled by adjusting the plurality of
couplings {.alpha..sub.j} in accordance with equations (2)-(3),
e.g. to provide an output wave with any desired polarization (e.g.
linear, circular, or elliptical).
Alternatively or additionally, for embodiments in which the
wave-propagating structure has a plurality of feeds (e.g. one feed
for each "finger" of an interdigital arrangement of one-dimensional
wave-propagating structures, as discussed above), a desired output
wave E(.theta.,.phi.) may be controlled by adjusting gains of
individual amplifiers for the plurality of feeds. Adjusting a gain
for a particular feed line would correspond to multiplying the
A.sub.j's by a gain factor G for those elements j that are fed by
the particular feed line. Especially, for approaches in which a
first wave-propagating structure having a first feed (or a first
set of such structures/feeds) is coupled to elements that are
selected from LP.sup.(1) and a second wave-propagating structure
having a second feed (or a second set of such structures/feeds) is
coupled to elements that are selected from LP.sup.(2),
depolarization loss (e.g., as a beam is scanned off-broadside) may
be compensated by adjusting the relative gain(s) between the first
feed(s) and the second feed(s).
As mentioned previously in the context of FIG. 1, in some
approaches the surface scattering antenna 100 includes a
wave-propagating structure 104 that may be implemented as a closed
waveguide (or a plurality of closed waveguides); and in these
approaches, the scattering elements may include complementary
metamaterial elements or patch elements. Exemplary closed
waveguides that include complementary metamaterial elements are
depicted in FIGS. 10 and 11 of A. Bily et al, previously cited.
Another exemplary closed waveguide embodiment that includes patch
elements is presently depicted in FIG. 5. In this embodiment, a
closed waveguide with a rectangular cross section is defined by a
trough 502 and a first printed circuit board 510 having three
layers: a lower conductor 512, a middle dielectric 514, and an
upper conductor 516. The upper and lower conductors may be
electrically connected by stitching vias (not shown). The trough
502 can be implemented as a piece of metal that is milled or cast
to provide the "floor and walls" of the closed waveguide, with the
first printed circuit board 510 providing the waveguide "ceiling."
Alternatively, the trough 502 may be implemented with an epoxy
laminate material (such as FR-4) in which the waveguide channel is
routed or machined and then plated (e.g. with copper) using a
process similar to a standard PCB through hole/via process.
Overlaid on the first printed circuit board 510 are a dielectric
spacer 520 and second printed circuit board 530. As the unit cell
cutaway shows, the conducting surface 516 has an iris 518 that
permits coupling between a guided wave and the resonator element
540, which in this case is a rectangular patch element disposed on
the lower surface of the second printed circuit board 530. A via
536 through the dielectric layer 534 of the second printed circuit
board 530 can be used to connect a bias voltage line 538 to the
patch element 540. The patch element 540 may be optionally bounded
by collonades of vias 550 extended through the dielectric layer 534
to reduce coupling or crosstalk between adjacent unit cells. The
dielectric spacer 520 includes a cutout region 525 between the iris
518 and the patch 540, and this cutout region is filled with an
electrically tunable medium (such as a liquid crystal medium) to
accomplish tuning of the cell resonance.
While the waveguide embodiment of FIG. 5 provides a waveguide
having a simple rectangular cross section, in some approaches the
waveguide may include one or more ridges (as in a double-ridged
waveguide). Ridged waveguides can provide greater bandwidth than
simple rectangular waveguides and the ridge geometries
(widths/heights) can be varied along the length of the waveguide to
control the couplings to the scattering elements (e.g. to enhance
aperture efficiency and/or control aperture tapering of the beam
profile) and/or to provide a smooth impedance transition (e.g. from
an SMA connector feed). Alternatively or additionally, the
waveguide may be loaded with a dielectric material (such as PTFE).
This dielectric material can occupy all or a portion of the
waveguide cross section, and the amount of the cross section that
is occupied can also be tapered along the length of the
waveguide.
While the example of FIG. 5 depicts a rectangular patch 540 fed by
a narrow iris 518, a variety of patch and iris geometries may be
used, with exemplary configurations depicted in FIG. 6A-6B. These
figures depict the placement of patches 601 and irises 602 when
viewed looking down upon a closed waveguide 610 having a center
axis 612. FIG. 6A shows rectangular patches 601 oriented along the
y-direction and edge-fed by slit-like irises 602 oriented along the
x-direction. FIG. 6B shows hexagonal patches 601 center-fed by
circular irises 602. The hexagonal patches may include notches 603
to adjust the resonant frequencies of the patches. It will be
appreciated that the irises and patches can take a variety of other
shapes including rectangles, squares, ellipses, circles, or
polygons, with or without notches or tabs to adjust resonant
frequencies, and that the relative lateral (x and/or y) position
between patch and iris may be adjusted to achieve a desired patch
response, e.g. edge-fed or center-fed. For example, an offset feed
may be used to stimulate circularly polarization radiation. The
positions, shapes, and/or sizes of the irises and/or patches can be
gradually adjusted or tapered along the length of the waveguide, to
control the waveguide couplings to the patch elements (e.g. to
enhance overall aperture efficiency and/or control aperture
tapering of the beam profile).
Because the irises 602 couple the patches 601 to the guided wave
mode by means of the H-field that is present at the upper surface
of the waveguide, the irises can be particularly positioned along
the y-direction (perpendicular to the waveguide) to exploit the
pattern of this H-field at the upper surface of the waveguide. FIG.
6C depicts this H-field pattern for the dominant TE10 mode of a
rectangular waveguide. On the center axis 612 of the waveguide, the
H-field is entirely directed along the x-direction, whereas at the
edge 614 of the waveguide, the H-field is entirely directed along
the y-direction. For a slit-like iris oriented along the
x-direction, the iris-mediated coupling between the patch and the
waveguide can be adjusted by changing the x-position of the iris;
thus, for example, slit-like irises can be positioned equidistant
from the center axis 612 on left and right sides of the waveguide
for equal coupling, as in FIG. 6A. This x-positioning of the irises
can also be gradually adjusted or tapered along the length of the
waveguide, to control the couplings to the patch elements (e.g. to
enhance overall aperture efficiency and/or control aperture
tapering of the beam profile).
For positions intermediate between the center axis 612 and the edge
614 in FIG. 6C, the H-field has both x and y components and sweeps
out an ellipse at a fixed iris location as the guided wave mode
propagates along the waveguide. Thus, the iris-mediated coupling
between the patch and the waveguide can be adjusted by changing the
x-position of the iris: changing the distance from the center axis
612 adjusts the eccentricity of the coupled H-field, which
switching from one side of the center axis to the other side
reverses the direction of rotation of the coupled H-field.
In one approach, the rotation of the H-field for a fixed position
away from the center axis 612 of the waveguide can be exploited to
provide a beam that is circularly polarized by virtue of this
H-field rotation. A patch with two resonant modes having mutually
orthogonal polarization states can leverage the rotation of the
H-field excitation to result in a circular or elliptical
polarization. For example, for a guided wave TE10 mode that
propagates in the +y direction of FIG. 6C, positioning an iris and
center-fed square or circular patch halfway between the center axis
and the left edge of the waveguide will yield a
right-circular-polarized radiation pattern for the patch, while
positioning the iris and center-fed square or circular patch
halfway between the center axis and the right edge of the waveguide
will yield a left-circular-polarized radiation pattern for the
patch. Thus, the antenna may be switched between polarization
states by switching from active elements on the left half of the
waveguide to active elements on the right half of the waveguide or
vice versa, or by reversing the direction of propagation of the
guided wave TE10 mode (e.g. by feeding the waveguide from the
opposite end).
Alternatively, for scattering elements that yield linear
polarization patterns, as for the configuration of FIG. 6A, the
linear polarization may be converted to circular polarization by
placing a linear-to-circular polarization conversion structure
above the scattering elements. For example, a quarter-wave plate or
meander-line structure may be positioned above the scattering
elements. Quarter-wave plates may include anisotropic dielectric
materials (see, e.g., H. S. Kirschbaum and S. Chen, "A Method of
Producing Broad-Band Circular Polarization Employing an Anisotropic
Dielectric," IRE Trans. Micro. Theory. Tech., Vol. 5, No. 3, pp.
199-203, 1957; J. Y. Chin et al, "An efficient broadband
metamaterial wave retarder," Optics Express, Vol. 17, No. 9, pp.
7640-7647, 2009), and/or may also be implemented as artificial
magnetic materials (see, e.g., Dunbao Yan et al, "A Novel
Polarization Convert Surface Based on Artificial Magnetic
Conductor," Asia-Pacific Microwave Conference Proceedings, 2005).
Meander-line polarizers typically consist of two, three, four, or
more layers of conducting meander line arrays (e.g. copper on a
thin dielectric substrate such as Duroid), with interleaved spacer
layers (e.g. closed-cell foam). Meander-line polarizers may be
designed and implemented according to known techniques, for example
as described in Young, et. al., "Meander-Line Polarizer," IEEE
Trans. Ant. Prop., pp. 376-378, May 1973 and in R. S. Chu and K. M.
Lee, "Analytical Model of a Multilayered Meander-Line Polarizer
Plate with Normal and Oblique Plane-Wave Incidence," IEEE Trans.
Ant. Prop., Vol. AP-35, No. 6, pp. 652-661, June 1987. In
embodiments that include a linear-to-circular polarization
conversion structure, the conversion structure may be incorporated
into, or may function as, a radome providing environmental
insulation for the antenna. Moreover, the conversion structure may
be flipped over to reverse the polarization state of the
transmitted or received radiation.
The electrically tunable medium that occupies the cutaway region
125 between the iris 118 and patch 140 in FIG. 6 may include a
liquid crystal. Liquid crystals have a permittivity that is a
function of orientation of the molecules comprising the liquid
crystal; and that orientation may be controlled by applying a bias
voltage (equivalently, a bias electric field) across the liquid
crystal; accordingly, liquid crystals can provide a voltage-tunable
permittivity for adjustment of the electromagnetic properties of
the scattering element. Exemplary liquid crystals that may be
deployed in various embodiments include 4-Cyano-4'-pentylbiphenyl
and high birefringence eutectic LC mixtures such as LCMS-107 (LC
Matter) or GT3-23001 (Merck).
Some approaches may utilize dual-frequency liquid crystals. In
dual-frequency liquid crystals, the liquid crystal director aligns
substantially parallel to an applied bias field at a lower
frequencies, but substantially perpendicular to an applied bias
field at higher frequencies. Accordingly, for approaches that
deploy these dual-frequency liquid crystals, tuning of the
scattering elements may be accomplished by adjusting the frequency
of the applied bias voltage signals.
Other approaches may deploy polymer network liquid crystals (PNLCs)
or polymer dispersed liquid crystals (PDLCs), which generally
provide much shorter relaxation/switching times for the liquid
crystal. An example is a thermal or UV cured mixture of a polymer
(such as BPA-dimethacrylate) in a nematic LC host (such as
LCMS-107); cf. Y. H. Fan et al, "Fast-response and scattering-free
polymer network liquid crystals for infrared light modulators,"
Applied Physics Letters 84, 1233-35 (2004), herein incorporated by
reference. Whether the polymer-liquid crystal mixture is described
as a PNLC or a PDLC depends upon the relative concentration of
polymer and liquid crystal, the latter having a higher
concentration of polymer whereby the LC is confined in the polymer
network as droplets.
Some approaches may include a liquid crystal that is embedded
within an interstitial medium. An example is a porous polymer
material (such as a PTFE membrane) impregnated with a nematic LC
(such as LCMS-107); cf. T. Kuki et al, "Microwave variable delay
line using a membrane impregnated with liquid crystal," Microwave
Symposium Digest, 2002 IEEE MTT-S International, vol. 1, pp.
363-366 (2002), herein incorporated by reference.
The interstitial medium is preferably a porous material that
provides a large surface area for strong surface alignment of the
unbiased liquid crystal. Examples of such porous materials include
ultra high molecular weight polyethylene (UHMW-PE) and expanded
polytetraflouroethylene (ePTFE) membranes that have been treated to
be hydrophilic. Specific examples of such interstitial media
include Advantec MFS Inc., Part # H020A047A (hydrophilic ePTFE) and
DeWal Industries 402P (UHMW-PE).
In the patch arrangement of FIG. 5, it may be seen that the voltage
biasing of the patch antenna relative to the conductive surface 516
containing the iris 518 will induce a substantially vertical
(z-direction) alignment of the liquid crystal that occupies the
cutaway region 525. Accordingly, to enhance the tuning effect, it
may be desirable to arrange the interstitial medium and/or
alignment layers to provide an unbiased liquid crystal alignment
that is substantially horizontal (e.g. in the y direction). An
example of such an arrangement is depicted in FIG. 7, which shows
an exploded diagram of the same elements as in FIG. 5. In this
example, the upper conductor 516 of the lower circuit board
presents a lower alignment layer 701 that is aligned along the
y-direction. This alignment layer may be implemented by, for
example, coating the lower circuit board with a polyimide layer and
rubbing or otherwise patterning (e.g. by machining or
photolithography) the polyimide layer to introduce microscopic
grooves that run parallel to the y-direction. Similarly, the upper
dielectric 534 and patch 540 present an upper alignment layer 702
that is also aligned along the y-direction. A
liquid-crystal-impregnated interstitial medium 703 fills the
cutaway region 525 of the spacer layer 520; as depicted
schematically in the figure, the interstitial medium may be
designed and arranged to include microscopic pores 710 that extend
along the y-direction to present a large surface area for the
liquid crystal that is substantially along the y-direction.
In some approaches, it may be desirable to introduce one or more
counter-electrodes into the unit cell, so that the unit cell can
provide both a first biasing that aligns the liquid crystal
substantially parallel to the electric field lines of the unit cell
resonance mode, and a second biasing ("counter-biasing") that
aligns the liquid crystal substantially perpendicular to the
electric field lines of the unit cell resonance mode. One advantage
of introducing counter-biasing is that that the unit cell tuning
speed is then no longer limited by a passive relaxation time of the
liquid crystal.
For purposes of characterizing counter-electrode arrangements, it
is useful to distinguish between in-plane switching schemes, where
the resonators are defined by conducting islands coplanar with a
ground plane (e.g. as with the so-called "CELC" resonators, such as
those described in A. Bily et al, previously cited), and vertical
switching schemes, where the resonators are defined by patches
positioned vertically above a ground plane containing irises (e.g.
as in FIG. 5).
A counter-electrode arrangement for an in-plane switching scheme is
depicted in FIG. 8A, which shows a unit cell resonator defined by
an inner electrode or conducting island 801 and an outer electrode
or ground plane 802. The liquid crystal material 810 is enclosed
above the resonator by an enclosing structure 820, e.g. a
polycarbonate container. In the exemplary counter-electrode
arrangement of FIG. 8A, the counter-electrode is provided as a very
thin layer 830 of a conducting material such as chromium or
titanium, deposited on the upper surface of the enclosing structure
820. The layer is thin enough (e.g. 10-30 nm) to introduce only
small loss at antenna operating frequencies, but sufficiently
conductive that the (1/RC) charging rate is small compared to the
unit cell update rate. In other approaches, the conducting layer is
an organic conductor such as polyacetylene, which can be
spin-coated on the enclosing structure 820. In yet other
approaches, the conducting layer is an anisotropic conducting
layer, i.e. having two conductivities .sigma..sub.1 and
.sigma..sub.2 for two orthogonal directions along the layer, and
the anisotropic conducting layer may be aligned relative to the
unit cell resonator so that the effective conductivity seen by the
unit cell resonator is minimized. For example, the anisotropic
conducting layer may consist of wires or stripes that are aligned
substantially perpendicular to the electric field lines of the unit
cell resonance mode.
By applying a first bias corresponding to a voltage differential
Vi-V0 between the inner electrode 801 and outer electrode 802, a
first (substantially horizontal) bias electric field 840 is
established, substantially parallel to electric field lines of the
unit cell resonance mode. On the other hand, by applying a second
bias corresponding to a voltage differential
V.sub.c-V.sub.i=V.sub.c-V.sub.o between the counter-electrode 830
and the inner and outer electrodes 801 and 802, a second
(substantially vertical) bias electric field 842 is established,
substantially perpendicular to electric field lines of the unit
cell resonance mode.
In some approaches, the second bias may be applied for a duration
shorter than a relaxation time of the liquid crystal; for example,
the second bias may be applied for less than one-half or one-third
of this relaxation time. One advantage of this approach is that
while the application of the second bias seeds the relaxation of
the liquid crystal, it may be preferable to have the liquid crystal
then relax to an unbiased state rather than align according to the
bias electric field.
A counter-electrode arrangement for a vertical switching scheme is
depicted in FIG. 8B, which shows a unit cell resonator defined by
an upper patch 804 and a lower ground plane 805 containing an iris
806. The liquid crystal material 810 is enclosed within the region
between the upper dielectric layer 808 (supporting the upper patch
804) and the lower dielectric layer 809 (supporting the lower
ground plane 805). In the exemplary counter-electrode arrangement
of FIG. 8B, the counter-electrode is provided as a very thin layer
830 of a conducting material such as chromium or titanium,
deposited on the lower surface of the upper dielectric layer 808.
The layer is thin enough (e.g. 10-30 nm) to introduce only small
loss at antenna operating frequencies, but sufficiently conductive
that the (1/RC) charging rate is small compared to the unit cell
update rate. Other approaches may use organic conductors or
anisotropic conducting layers, as described above.
By applying a first bias corresponding to a voltage differential
V.sub.u-V.sub.l=V.sub.c-V.sub.l between the upper and counter
electrodes 804 and 830 and lower electrode 805, a first
(substantially vertical) bias electric field 844 is established,
substantially parallel to electric field lines of the unit cell
resonance mode. On the other hand, by applying a second bias
corresponding to a voltage differential V.sub.c-V.sub.u between the
counter electrode 830 and the upper electrode 804, a second
(substantially horizontal) bias electric field 846 is established,
substantially perpendicular to electric field lines of the unit
cell resonance mode. Again, in some approaches, the second bias may
be applied for a duration shorter than a relaxation time of the
liquid crystal, for the same reason as discussed above for
horizontal switching. In various embodiments of the vertical
switching scheme, the counter-electrode 830 may constitute a pair
of electrodes on opposite sides of the patch 804, or a U-shaped
electrode that surrounds three sides of the patch 804, or a closed
loop that surrounds all four sides of the patch 804.
In various approaches, the bias voltage lines may be directly
addressed, e.g. by extending a bias voltage line for each
scattering element to a pad structure for connection to antenna
control circuitry, or matrix addressed, e.g. by providing each
scattering element with a voltage bias circuit that is addressable
by row and column. FIG. 9 depicts an example of a configuration
that provides direct addressing for an arrangement of scattering
elements 900, in which a plurality of bias voltage lines 904
deliver individual bias voltages to the scattering elements. FIG.
10 depicts an example of a configuration that provides matrix
addressing for an arrangement of scattering elements 1000, where
each scattering element is connected by a bias voltage line 1002 to
a biasing circuit 1004 addressable by row inputs 1006 and column
inputs 1008 (note that each row input and/or column input may
include one or more signals, e.g. each row or column may be
addressed by a single wire or a set of parallel wires dedicated to
that row or column). Each biasing circuit may contain, for example,
a switching device (e.g. a transistor), a storage device (e.g. a
capacitor), and/or additional circuitry such as logic/multiplexing
circuitry, digital-to-analog conversion circuitry, etc. This
circuitry may be readily fabricated using monolithic integration,
e.g. using a thin-film transistor (TFT) process, or as a hybrid
assembly of integrated circuits that are mounted on the
wave-propagating structure, e.g. using surface mount technology
(SMT). Although FIGS. 9 and 10 depict the scattering elements as
"CELC" resonators, this depiction is intended to represent generic
scattering elements, and the direct or matrix addressing schemes of
FIGS. 9 and 10 are applicable to other unit cell designs (such as
the patch element).
For approaches that use liquid crystal as a tunable medium for the
unit cell, it may be desirable to provide unit cell bias voltages
that are AC signals with a minimal DC component. Prolonged DC
operation can cause electrochemical reactions that significantly
reduce the usable lifespan of the liquid crystal as a tunable
medium. In some approaches, a unit cell may be tuned by adjusting
the amplitude of an AC bias signal. In other approaches, a unit
cell may be tuned by adjusting the pulse width of an AC bias
signal, e.g. using pulse width modulation (PWM). In yet other
approaches, a unit cell may be tuned by adjusting both the
amplitude and pulse with of an AC bias signal. Various liquid
crystal drive schemes have been extensively explored in the liquid
crystal display literature, for example as described in Robert
Chen, Liquid Crystal Displays, Wiley, N.J., 2011, and in Willem den
Boer, Active Matrix Liquid Crystal Displays, Elsevier, Burlington,
Mass. 2009.
Exemplary waveforms for a binary (ON-OFF) bias voltage adjustment
scheme are depicted in FIG. 11A. In this binary scheme, a first
square wave voltage V.sub.i is applied to inner electrode 1111 of a
unit cell 1110, and a second square wave voltage V.sub.o is applied
to outer electrode 1112 of the unit cell. Although the figure
depicts a "CELC" resonator defined by a conducting island (inner
electrode) coplanar with a ground plane (outer electrode), this
depiction is intended to represent a generic unit cell, and the
drive scheme is applicable to other unit cell designs. For example,
for a "patch" resonator defined by a conducting patch positioned
vertically above an iris in a ground plane, the first square wave
voltage V.sub.i may be applied to the patch, while the second
square wave voltage V.sub.o may be applied to the ground plane.
In the binary scheme of FIG. 11A, the unit cell is biased "ON" when
the two square waves are 180.degree. out of phase with each other,
with the result that the potential applied to the liquid crystal,
V.sub.LC=V.sub.i-V.sub.o, is a square wave with zero DC offset, as
shown in the top right panel of the figure. On the other hand, the
unit cell is biased "OFF" when the two square waves are in phase
with each other, with the result that V.sub.LC=0, as shown in the
bottom right panel of the figure. The square wave amplitude VPP is
a voltage large enough to effect rapid alignment of the liquid
crystal, typically in the range of 10-100 volts. The square wave
frequency is a "drive" frequency that is large compared to both the
desired antenna switching rate and liquid crystal relaxation rates.
The drive frequency can range from as low as 10 Hz to as high as
100 kHz.
Exemplary circuitry providing the waveforms of FIG. 11A to a
plurality of unit cells is depicted in FIG. 1B. In this example,
bits representing the "ON" or "OFF" states of the unit cells are
read into a N-bit serial-to-parallel shift register 1120 using the
DATA and CLK signals. When this serial read-in is complete, the
LATCH signal is triggered to store these bits in an N-bit latch
1130. The N-bit latch outputs, which may be toggled with XOR gates
1140 via the POL signal, provide the inputs for high-voltage
push-pull amplifiers 1150 that deliver the waveforms to the unit
cells. Note that one or more bits of the shift register may be
reserved to provide the waveform for the common outer electrode
1162, while the remaining bits of the shift register provide the
individual waveforms for the inner electrodes 1161 of the unit
cells. Alternatively, the entire shift register may be used for
inner electrodes 1161, and a separate push-pull amplifier may be
used for the outer electrode 1162. Square waves may be produced at
the outputs of the push-pull amplifiers 1150 by either (1) toggling
the XOR gates at the drive frequency (i.e. with a POL signal that
is a square wave at the drive frequency) or (2) latching at twice
the drive frequency (i.e. with a LATCH signal that is a square wave
at twice the drive frequency) while reading in complementary bits
during the second half-cycle of each drive period. Under the latter
approach, because there is an N-bit read-in during each half-cycle
of the drive period, the serial input data is clocked at a
frequency not less than 2.times.N.times.f where f is the drive
frequency. The N-bit shift register may address all of the unit
cells that compose the antenna, or several N-bit shift registers
may be used, each addressing a subset of the unit cells.
The binary scheme of FIG. 11A applies voltage waveforms to both the
inner and outer electrode of the unit cell. In another approach,
shown in FIG. 12A, the outer electrode is grounded and a voltage
waveform is applied only to the inner electrode of the unit cell.
In this single-ended drive approach, the unit cell is biased "ON"
when a square wave with zero DC offset is applied to the inner
electrode 1111 (as shown in the top right panel of FIG. 12A) and
biased "OFF" when a zero voltage is applied to the inner electrode
(as shown in the bottom right panel of FIG. 12A).
Exemplary circuitry providing the waveforms of FIG. 12A to a
plurality of unit cells is depicted in FIG. 12B. The circuitry is
similar to that of FIG. 1B, except that the common outer electrode
is now grounded, and new oscillating power supply voltages VPP' and
VDD' are used for the high-voltage circuits and the digital
circuits, respectively, with the ground terminals of these circuits
being connected to a new negative oscillating power supply voltage
VNN'. Exemplary waveforms for these oscillating power supply
voltages are shown in the lower panel of the figure. Note that
these oscillating power supply voltages preserve the voltage
differentials VPP'-VNN'=VPP and VDD'-VNN'=VDD, where VPP is the
desired amplitude of the voltage V.sub.LC applied to the liquid
crystal, and VDD is the power supply voltage for the digital
circuitry. For the digital inputs to operate properly with these
oscillating power supplies, the single-ended drive circuitry also
includes voltage-shifting circuitry 1200 presenting these digital
inputs as signals relative to VNN' rather than GND.
Exemplary waveforms for a grayscale voltage adjustment scheme are
depicted in FIG. 13. In this grayscale scheme, a first square wave
voltage V.sub.i is again applied to inner electrode 1111 of a unit
cell 1110 and a second square wave voltage V.sub.o is again applied
to outer electrode 1112 of the unit cell. A desired gray level is
then achieved by selecting a phase difference between the two
square waves. In one approach, as shown in FIG. 13, the drive
period is divided into a discrete set of time slices corresponding
to a discrete set of phase differences between the two square
waves. In the nonlimiting example of FIG. 13, there are eight (8)
time slices, providing five (5) gray levels corresponding to phase
differences of 0.degree., 45.degree., 90.degree., 135.degree., and
180.degree.. The figure depicts two gray level examples: for a
phase difference of 45.degree., as shown in the upper right panel
of the figure, the potential applied to the liquid crystal,
V.sub.LC=V.sub.i-V.sub.o, is an alternating pulse train with zero
DC offset and an RMS voltage of VPP/4; for a phase difference of
90.degree., as shown in the lower right panel of the figure,
V.sub.LC is an alternating pulse train with zero DC offset and an
RMS voltage of VPP/2. Thus, the gray level scheme of FIG. 13
provides a pulse-width modulated (PWM) liquid crystal waveform with
zero DC offset and an adjustable RMS voltage.
The drive circuitry of FIG. 1B may be used to provide the grayscale
waveforms of FIG. 13 to a plurality of unit cells. However, for a
grayscale implementation, an N-bit read-in is completed during each
time slice of the drive period. Thus, for an implementation with T
time slices (corresponding to (T/2)+1 gray levels), the serial
input data is clocked at a frequency not less than
T.times.N.times.f, where f is the drive frequency (it will be
appreciated that T=2 corresponds to the binary drive scheme of FIG.
11A).
With reference now to FIG. 14, an illustrative embodiment is
depicted as a system block diagram. The system 1400 include a
communications unit 1410 coupled by one or more feeds 1412 to an
antenna unit 1420. The communications unit 1410 might include, for
example, a mobile broadband satellite transceiver, or a
transmitter, receiver, or transceiver module for a radio or
microwave communications system, and may incorporate data
multiplexing/demultiplexing circuitry, encoder/decoder circuitry,
modulator/demodulator circuitry, frequency
upconverters/downconverters, filters, amplifiers, diplexes, etc.
The antenna unit includes at least one surface scattering antenna,
which may be configured to transmit, receive, or both; and in some
approaches the antenna unit 1420 may comprise multiple surface
scattering antennas, e.g. first and second surface scattering
antennas respectively configured to transmit and receive. For
embodiments having a surface scattering antenna with multiple
feeds, the communications unit may include MIMO circuitry. The
system 1400 also includes an antenna controller 1430 configured to
provide control input(s) 1432 that determine the configuration of
the antenna. For example, the control inputs(s) may include inputs
for each of the scattering elements (e.g. for a direct addressing
configuration such as depicted in FIG. 12), row and column inputs
(e.g. for a matrix addressing configuration such as that depicted
in FIG. 13), adjustable gains for the antenna feeds, etc.
In some approaches, the antenna controller 1430 includes circuitry
configured to provide control input(s) 1432 that correspond to a
selected or desired antenna radiation pattern. For example, the
antenna controller 1430 may store a set of configurations of the
surface scattering antenna, e.g. as a lookup table that maps a set
of desired antenna radiation patterns (corresponding to various
beam directions, beams widths, polarization states, etc. as
discussed earlier in this disclosure) to a corresponding set of
values for the control input(s) 1432. This lookup table may be
previously computed, e.g. by performing full-wave simulations of
the antenna for a range of values of the control input(s) or by
placing the antenna in a test environment and measuring the antenna
radiation patterns corresponding to a range of values of the
control input(s). In some approaches the antenna controller may be
configured to use this lookup table to calculate the control
input(s) according to a regression analysis; for example, by
interpolating values for the control input(s) between two antenna
radiation patterns that are stored in the lookup table (e.g. to
allow continuous beam steering when the lookup table only includes
discrete increments of a beam steering angle). The antenna
controller 1430 may alternatively be configured to dynamically
calculate the control input(s) 1432 corresponding to a selected or
desired antenna radiation pattern, e.g. by computing a holographic
pattern corresponding to an interference term Re[.PSI..sub.out
.PSI.*.sub.in] (as discussed earlier in this disclosure), or by
computing the couplings {.alpha..sub.j} (corresponding to values of
the control input(s)) that provide the selected or desired antenna
radiation pattern in accordance with equation (1) presented earlier
in this disclosure.
In some approaches the antenna unit 1420 optionally includes a
sensor unit 1422 having sensor components that detect environmental
conditions of the antenna (such as its position, orientation,
temperature, mechanical deformation, etc.). The sensor components
can include one or more GPS devices, gyroscopes, thermometers,
strain gauges, etc., and the sensor unit may be coupled to the
antenna controller to provide sensor data 1424 so that the control
input(s) 1432 may be adjusted to compensate for translation or
rotation of the antenna (e.g. if it is mounted on a mobile platform
such as an aircraft) or for temperature drift, mechanical
deformation, etc.
In some approaches the communications unit may provide feedback
signal(s) 1434 to the antenna controller for feedback adjustment of
the control input(s). For example, the communications unit may
provide a bit error rate signal and the antenna controller may
include feedback circuitry (e.g. DSP circuitry) that adjusts the
antenna configuration to reduce the channel noise. Alternatively or
additionally, for pointing or steering applications the
communications unit may provide a beacon signal (e.g. from a
satellite beacon) and the antenna controller may include feedback
circuitry (e.g. pointing lock DSP circuitry for a mobile broadband
satellite transceiver).
An illustrative embodiment is depicted as a process flow diagram in
FIG. 15. Flow 1500 includes operation 1510--selecting a first
antenna radiation pattern for a surface scattering antenna that is
adjustable responsive to one or more control inputs. For example,
an antenna radiation pattern may be selected that directs a primary
beam of the radiation pattern at the location of a
telecommunications satellite, a telecommunications base station, or
a telecommunications mobile platform. Alternatively or
additionally, an antenna radiation pattern may be selected to place
nulls of the radiation pattern at desired locations, e.g. for
secure communications or to remove a noise source. Alternatively or
additionally, an antenna radiation pattern may be selected to
provide a desired polarization state, such as circular polarization
(e.g. for Ka-band satellite communications) or linear polarization
(e.g. for Ku-band satellite communications). Flow 1500 includes
operation 1520--determining first values of the one or more control
inputs corresponding to the first selected antenna radiation
pattern. For example, in the system of FIG. 14, the antenna
controller 1430 can include circuitry configured to determine
values of the control inputs by using a lookup table, or by
computing a hologram corresponding to the desired antenna radiation
pattern. Flow 1500 optionally includes operation 1530--providing
the first values of the one or more control inputs for the surface
scattering antenna. For example, the antenna controller 1430 can
apply bias voltages to the various scattering elements, and/or the
antenna controller 1430 can adjust the gains of antenna feeds. Flow
1500 optionally includes operation 1540--selecting a second antenna
radiation pattern different from the first antenna radiation
pattern. Again, this can include selecting, for example, a second
beam direction or a second placement of nulls. In one application
of this approach, a satellite communications terminal can switch
between multiple satellites, e.g. to optimize capacity during peak
loads, to switch to another satellite that may have entered
service, or to switch from a primary satellite that has failed or
is off-line. Flow 1500 optionally includes operation
1550--determining second values of the one or more control inputs
corresponding to the second selected antenna radiation pattern.
Again this can include, for example, using a lookup table or
computing a holographic pattern. Flow 1500 optionally includes
operation 1560--providing the second values of the one or more
control inputs for the surface scattering antenna. Again this can
include, for example, applying bias voltages and/or adjusting feed
gains.
Another illustrative embodiment is depicted as a process flow
diagram in FIG. 16. Flow 1600 includes operation 1610--identifying
a first target for a first surface scattering antenna, the first
surface scattering antenna having a first adjustable radiation
pattern responsive to one or more first control inputs. This first
target could be, for example, a telecommunications satellite, a
telecommunications base station, or a telecommunications mobile
platform. Flow 1600 includes operation 1620--repeatedly adjusting
the one or more first control inputs to provide a substantially
continuous variation of the first adjustable radiation pattern
responsive to a first relative motion between the first target and
the first surface scattering antenna. For example, in the system of
FIG. 14, the antenna controller 1430 can include circuitry
configured to steer a radiation pattern of the surface scattering
antenna, e.g. to track the motion of a non-geostationary satellite,
to maintain pointing lock with a geostationary satellite from a
mobile platform (such as an airplane or other vehicle), or to
maintain pointing lock when both the target and the antenna are
moving. Flow 1600 optionally includes operation 1630--identifying a
second target for a second surface scattering antenna, the second
surface scattering antenna having a second adjustable radiation
pattern responsive to one or more second control inputs; and flow
1600 optionally includes operation 1640--repeatedly adjusting the
one or more second control inputs to provide a substantially
continuous variation of the second adjustable radiation pattern
responsive to a relative motion between the second target and the
second surface scattering antenna. For example, some applications
may deploy both a primary antenna unit, tracking a first object
(such as a first non-geostationary satellite), and a secondary or
auxiliary antenna unit, tracking a second object (such as a second
non-geostationary satellite). In some approaches the auxiliary
antenna unit may include a smaller-aperture antenna (tx and/or rx)
primarily used to track the location of the secondary object (and
optionally to secure a link to the secondary object at a reduced
quality-of-service (QoS)). Flow 1600 optionally includes operation
1650--adjusting the one or more first control inputs to place the
second target substantially within the primary beam of the first
adjustable radiation pattern. For example, in an application in
which the first and second antennas are components of a satellite
communications terminal that interacts with a constellation of
non-geostationary satellites, the first or primary antenna may
track a first member of the satellite constellation until the first
member approaches the horizon (or the first antenna suffers
appreciable scan loss), at which time a "handoff" is accomplished
by switching the first antenna to track the second member of the
satellite constellation (which was being tracked by the second or
auxiliary antenna). Flow 1600 optionally includes operation
1660--identifying a new target for a second surface scattering
antenna different from the first and second targets; and flow 1600
optionally includes operation 1670--adjusting the one or more
second control inputs to place the new target substantially within
the primary beam of the second adjustable radiation pattern. For
example, after the "handoff," the secondary or auxiliary antenna
can initiate a link with a third member of the satellite
constellation (e.g. as it rises above the horizon).
FIGS. 19 and 20 provide respective general descriptions of several
environments in which implementations may be implemented. FIG. 17
is generally directed toward a thin computing environment 1719
having a thin computing device 1720, and FIG. 18 is generally
directed toward a general purpose computing environment 1800 having
general purpose computing device 1810. However, as prices of
computer components drop and as capacity and speeds increase, there
is not always a bright line between a thin computing device and a
general purpose computing device. Further, there is a continuous
stream of new ideas and applications for environments benefited by
use of computing power. As a result, nothing should be construed to
limit disclosed subject matter herein to a specific computing
environment unless limited by express language.
FIG. 17 and the following discussion are intended to provide a
brief, general description of a thin computing environment 1719 in
which embodiments may be implemented. FIG. 17 illustrates an
example system that includes a thin computing device 1720, which
may be included or embedded in an electronic device that also
includes a device functional element 1750. For example, the
electronic device may include any item having electrical or
electronic components playing a role in a functionality of the
item, such as for example, a refrigerator, a car, a digital image
acquisition device, a camera, a cable modem, a printer an
ultrasound device, an x-ray machine, a non-invasive imaging device,
or an airplane. For example, the electronic device may include any
item that interfaces with or controls a functional element of the
item. In another example, the thin computing device may be included
in an implantable medical apparatus or device. In a further
example, the thin computing device may be operable to communicate
with an implantable or implanted medical apparatus. For example, a
thin computing device may include a computing device having limited
resources or limited processing capability, such as a limited
resource computing device, a wireless communication device, a
mobile wireless communication device, a smart phone, an electronic
pen, a handheld electronic writing device, a scanner, a cell phone,
a smart phone (such as an Android.RTM. or iPhone.RTM. based
device), a tablet device (such as an iPad.RTM.) or a
Blackberry.RTM. device. For example, a thin computing device may
include a thin client device or a mobile thin client device, such
as a smart phone, tablet, notebook, or desktop hardware configured
to function in a virtualized environment.
The thin computing device 1720 includes a processing unit 1721, a
system memory 1722, and a system bus 1723 that couples various
system components including the system memory 1722 to the
processing unit 1721. The system bus 1723 may be any of several
types of bus structures including a memory bus or memory
controller, a peripheral bus, and a local bus using any of a
variety of bus architectures. The system memory includes read-only
memory (ROM) 1724 and random access memory (RAM) 1725. A basic
input/output system (BIOS) 1726, containing the basic routines that
help to transfer information between sub-components within the thin
computing device 1720, such as during start-up, is stored in the
ROM 1724. A number of program modules may be stored in the ROM 1724
or RAM 1725, including an operating system 1728, one or more
application programs 1729, other program modules 1730 and program
data 1731.
A user may enter commands and information into the computing device
1720 through one or more input interfaces. An input interface may
include a touch-sensitive screen or display surface, or one or more
switches or buttons with suitable input detection circuitry. A
touch-sensitive screen or display surface is illustrated as a
touch-sensitive display 1732 and screen input detector 1733. One or
more switches or buttons are illustrated as hardware buttons 1744
connected to the system via a hardware button interface 1745. The
output circuitry of the touch-sensitive display 1732 is connected
to the system bus 1723 via a video driver 1737. Other input devices
may include a microphone 1734 connected through a suitable audio
interface 1735, or a physical hardware keyboard (not shown). Output
devices may include the display 1732, or a projector display
1736.
In addition to the display 1732, the computing device 1720 may
include other peripheral output devices, such as at least one
speaker 1738. Other external input or output devices 1739, such as
a joystick, game pad, satellite dish, scanner or the like may be
connected to the processing unit 1721 through a USB port 1740 and
USB port interface 1741, to the system bus 1723. Alternatively, the
other external input and output devices 1739 may be connected by
other interfaces, such as a parallel port, game port or other port.
The computing device 1720 may further include or be capable of
connecting to a flash card memory (not shown) through an
appropriate connection port (not shown). The computing device 1720
may further include or be capable of connecting with a network
through a network port 1742 and network interface 1743, and through
wireless port 1746 and corresponding wireless interface 1747 may be
provided to facilitate communication with other peripheral devices,
including other computers, printers, and so on (not shown). It will
be appreciated that the various components and connections shown
are examples and other components and means of establishing
communication links may be used.
The computing device 1720 may be primarily designed to include a
user interface. The user interface may include a character, a
key-based, or another user data input via the touch sensitive
display 1732. The user interface may include using a stylus (not
shown). Moreover, the user interface is not limited to an actual
touch-sensitive panel arranged for directly receiving input, but
may alternatively or in addition respond to another input device
such as the microphone 1734. For example, spoken words may be
received at the microphone 1734 and recognized. Alternatively, the
computing device 1720 may be designed to include a user interface
having a physical keyboard (not shown).
The device functional elements 1750 are typically application
specific and related to a function of the electronic device, and
are coupled with the system bus 1723 through an interface (not
shown). The functional elements may typically perform a single
well-defined task with little or no user configuration or setup,
such as a refrigerator keeping food cold, a cell phone connecting
with an appropriate tower and transceiving voice or data
information, a camera capturing and saving an image, or
communicating with an implantable medical apparatus.
In certain instances, one or more elements of the thin computing
device 1720 may be deemed not necessary and omitted. In other
instances, one or more other elements may be deemed necessary and
added to the thin computing device.
FIG. 18 and the following discussion are intended to provide a
brief, general description of an environment in which embodiments
may be implemented. FIG. 18 illustrates an example embodiment of a
general-purpose computing system in which embodiments may be
implemented, shown as a computing system environment 1800.
Components of the computing system environment 1800 may include,
but are not limited to, a general purpose computing device 1810
having a processor 1820, a system memory 1830, and a system bus
1821 that couples various system components including the system
memory to the processor 1820. The system bus 1821 may be any of
several types of bus structures including a memory bus or memory
controller, a peripheral bus, and a local bus using any of a
variety of bus architectures. By way of example, and not
limitation, such architectures include Industry Standard
Architecture (ISA) bus, Micro Channel Architecture (MCA) bus,
Enhanced ISA (EISA) bus, Video Electronics Standards Association
(VESA) local bus, and Peripheral Component Interconnect (PCI) bus,
also known as Mezzanine bus.
The computing system environment 1800 typically includes a variety
of computer-readable media products. Computer-readable media may
include any media that can be accessed by the computing device 1810
and include both volatile and nonvolatile media, removable and
non-removable media. By way of example, and not of limitation,
computer-readable media may include computer storage media. By way
of further example, and not of limitation, computer-readable media
may include a communication media.
Computer storage media includes volatile and nonvolatile, removable
and non-removable media implemented in any method or technology for
storage of information such as computer-readable instructions, data
structures, program modules, or other data. Computer storage media
includes, but is not limited to, random-access memory (RAM),
read-only memory (ROM), electrically erasable programmable
read-only memory (EEPROM), flash memory, or other memory
technology, CD-ROM, digital versatile disks (DVD), or other optical
disk storage, magnetic cassettes, magnetic tape, magnetic disk
storage, or other magnetic storage devices, or any other medium
which can be used to store the desired information and which can be
accessed by the computing device 1810. In a further embodiment, a
computer storage media may include a group of computer storage
media devices. In another embodiment, a computer storage media may
include an information store. In another embodiment, an information
store may include a quantum memory, a photonic quantum memory, or
atomic quantum memory. Combinations of any of the above may also be
included within the scope of computer-readable media. Computer
storage media is a non-transitory computer-readable media.
Communication media may typically embody computer-readable
instructions, data structures, program modules, or other data in a
modulated data signal such as a carrier wave or other transport
mechanism and include any information delivery media. The term
"modulated data signal" means a signal that has one or more of its
characteristics set or changed in such a manner as to encode
information in the signal. By way of example, and not limitation,
communications media may include wired media, such as a wired
network and a direct-wired connection, and wireless media such as
acoustic, RF, optical, and infrared media. Communication media is a
transitory computer-readable media.
The system memory 1830 includes computer storage media in the form
of volatile and nonvolatile memory such as ROM 1831 and RAM 1832. A
RAM may include at least one of a DRAM, an EDO DRAM, a SDRAM, a
RDRAM, a VRAM, or a DDR DRAM. A basic input/output system (BIOS)
1833, containing the basic routines that help to transfer
information between elements within the computing device 1810, such
as during start-up, is typically stored in ROM 1831. RAM 1832
typically contains data and program modules that are immediately
accessible to or presently being operated on by the processor 1820.
By way of example, and not limitation, FIG. 18 illustrates an
operating system 1834, application programs 1835, other program
modules 1836, and program data 1837. Often, the operating system
1834 offers services to applications programs 1835 by way of one or
more application programming interfaces (APIs) (not shown). Because
the operating system 1834 incorporates these services, developers
of applications programs 1835 need not redevelop code to use the
services. Examples of APIs provided by operating systems such as
Microsoft's "WINDOWS" .RTM. are well known in the art.
The computing device 1810 may also include other
removable/non-removable, volatile/nonvolatile computer storage
media products. By way of example only, FIG. 18 illustrates a
non-removable non-volatile memory interface (hard disk interface)
1840 that reads from and writes for example to non-removable,
non-volatile magnetic media. FIG. 18 also illustrates a removable
non-volatile memory interface 1850 that, for example, is coupled to
a magnetic disk drive 1851 that reads from and writes to a
removable, non-volatile magnetic disk 1852, or is coupled to an
optical disk drive 1855 that reads from and writes to a removable,
non-volatile optical disk 1856, such as a CD ROM. Other
removable/non-removable, volatile/non-volatile computer storage
media that can be used in the example operating environment
include, but are not limited to, magnetic tape cassettes, memory
cards, flash memory cards, DVDs, digital video tape, solid state
RAM, and solid state ROM. The hard disk drive 1841 is typically
connected to the system bus 1821 through a non-removable memory
interface, such as the interface 1840, and magnetic disk drive 1851
and optical disk drive 1855 are typically connected to the system
bus 1821 by a removable non-volatile memory interface, such as
interface 1850.
The drives and their associated computer storage media discussed
above and illustrated in FIG. 18 provide storage of
computer-readable instructions, data structures, program modules,
and other data for the computing device 1810. In FIG. 18, for
example, hard disk drive 1841 is illustrated as storing an
operating system 1844, application programs 1845, other program
modules 1846, and program data 1847. Note that these components can
either be the same as or different from the operating system 1834,
application programs 1835, other program modules 1836, and program
data 1837. The operating system 1844, application programs 1845,
other program modules 1846, and program data 1847 are given
different numbers here to illustrate that, at a minimum, they are
different copies.
A user may enter commands and information into the computing device
1810 through input devices such as a microphone 1863, keyboard
1862, and pointing device 1861, commonly referred to as a mouse,
trackball, or touch pad. Other input devices (not shown) may
include at least one of a touch-sensitive screen or display
surface, joystick, game pad, satellite dish, and scanner. These and
other input devices are often connected to the processor 1820
through a user input interface 1860 that is coupled to the system
bus, but may be connected by other interface and bus structures,
such as a parallel port, game port, or a universal serial bus
(USB).
A display 1891, such as a monitor or other type of display device
or surface may be connected to the system bus 1821 via an
interface, such as a video interface 1890. A projector display
engine 1892 that includes a projecting element may be coupled to
the system bus. In addition to the display, the computing device
1810 may also include other peripheral output devices such as
speakers 1897 and printer 1896, which may be connected through an
output peripheral interface 1895.
The computing system environment 1800 may operate in a networked
environment using logical connections to one or more remote
computers, such as a remote computer 1880. The remote computer 1880
may be a personal computer, a server, a router, a network PC, a
peer device, or other common network node, and typically includes
many or all of the elements described above relative to the
computing device 1810, although only a memory storage device 1881
has been illustrated in FIG. 18. The network logical connections
depicted in FIG. 18 include a local area network (LAN) and a wide
area network (WAN), and may also include other networks such as a
personal area network (PAN) (not shown). Such networking
environments are commonplace in offices, enterprise-wide computer
networks, intranets, and the Internet.
When used in a networking environment, the computing system
environment 1800 is connected to the network 1871 through a network
interface, such as the network interface 1870, the modem 1872, or
the wireless interface 1893. The network may include a LAN network
environment, or a WAN network environment, such as the Internet. In
a networked environment, program modules depicted relative to the
computing device 1810, or portions thereof, may be stored in a
remote memory storage device. By way of example, and not
limitation, FIG. 18 illustrates remote application programs 1885 as
residing on memory storage device 1881. It will be appreciated that
the network connections shown are examples and other means of
establishing a communication link between the computers may be
used.
In certain instances, one or more elements of the computing device
1810 may be deemed not necessary and omitted. In other instances,
one or more other elements may be deemed necessary and added to the
computing device.
FIG. 19 illustrates an environment 1900 in which embodiments may be
implemented. The environment includes a horizon 1998 (which may be
the earth's horizon), at least two spaceborne sources transmitting
a target signal, illustrated by spaceborne sources 1992 and 1994
respectively transmitting target signals 1993 and 1995. The
environment includes a terrestrial source transmitting a possible
interfering signal, illustrated by vehicle 1996 transmitting
possible interfering signal 1997. The environment includes an
antenna system 1905, and an associated antenna 1980.
The antenna system 1905 includes a surface scattering antenna 1910.
The surface scattering antenna includes an electromagnetic
waveguide structure 1918 and a plurality of electromagnetic wave
scattering elements 1912 distributed along the waveguide structure.
The wave scattering elements have an inter-element spacing that is
substantially less than a free-space wavelength of a highest
operating frequency of the surface scattering antenna. Each
electromagnetic wave scattering element of the plurality of
electromagnetic wave scattering elements has a respective
activatable electromagnetic response to a guided wave propagating
in the waveguide structure. The plurality of electromagnetic wave
scattering elements are operable in combination to produce a
controllable radiation pattern, illustrated by a radiation pattern
1919. In an embodiment, the controllable radiation pattern includes
a controllable gain pattern. In an embodiment, a radiation pattern
refers to a distribution of gain in an antenna. The antenna system
includes antenna system components 1920.
FIG. 20 schematically illustrates components 1920 of the antenna
system 1905. The components include a gain definition circuit 1930
configured to define a radiation pattern 1919 configured to receive
a possible interfering signal 1997 transmitted within an operating
frequency band of an associated antenna 1980. FIG. 21 schematically
illustrates fields of view of the surface scattering antenna 1910
and the associated antenna. The associated antenna has a field of
view 1986 that includes a desired field of view 1987 and an
undesired field of view 1988. The surface scattering antenna has a
field of view 1916 that includes or covers at least a portion of
the undesired field of view of the associated antenna. The defined
antenna radiation pattern includes a field of view covering or
including at least a portion of the undesired field of view of the
associated antenna.
Returning to FIG. 20, the components 1920 of the antenna system
1905 include an antenna controller 1940 configured to establish the
defined radiation pattern 1919 in the surface scattering antenna
1910 by activating the respective electromagnetic response of
selected electromagnetic wave scattering elements of the plurality
of electromagnetic wave scattering elements 1912. In an embodiment,
the activating the respective electromagnetic response of selected
electromagnetic wave scattering elements may be considered as
establishing a hologram corresponding to the defined radiation
pattern. The components of the antenna system include a correction
circuit 1950 configured to reduce an influence of the received
possible interfering signal 1997 in a contemporaneously received
signal 1993 by the associated antenna 1980.
In an embodiment, the surface scattering antenna 1910 includes a
surface scattering antenna having a thin or narrow planar dimension
relative to a planar dimension of the associated antenna 1980. For
example, a major planar dimension of the surface scattering antenna
may be less than 20% of a major planar dimension of the associated
antenna. In an embodiment, the aperture of the surface scattering
antenna is less than 50% of the aperture of the associated antenna.
In an embodiment, the aperture of the surface scattering antenna is
less than 25% of the aperture of the associated antenna. In an
embodiment, the surface scattering antenna includes a surface
scattering antenna configured to generate an adjustable or
reconfigurable radiation pattern 1919. In an embodiment, the
surface scattering antenna includes an omnidirectional or
bidirectional surface scattering antenna. In an embodiment, the
surface scattering antenna includes a planar surface scattering
antenna. In an embodiment, the surface scattering antenna includes
a non-planar surface scattering antenna.
In an embodiment, the electromagnetic wave scattering elements 1912
include discrete electromagnetic wave scattering elements. In an
embodiment, the electromagnetic wave scattering elements include
electromagnetic wave scattering or radiating elements. In an
embodiment, the electromagnetic wave scattering elements include
metamaterial wave scattering elements. In an embodiment, the
electromagnetic wave scattering elements include electromagnetic
wave transmitting elements. In an embodiment, the electromagnetic
wave scattering elements include electromagnetic wave receiving
elements. In an embodiment, the electromagnetic wave scattering
elements are exposed to a propagation path of the electromagnetic
waveguide structure 1918. In an embodiment, the electromagnetic
wave scattering elements include electromagnetic wave scattering
elements respectively having at least two individually adjustable
electromagnetic responses to a guided wave propagating in the
waveguide structure. In an embodiment, the inter-element spacing of
the electromagnetic scattering elements includes at least three
electromagnetic scattering elements per the free-space wavelength.
In an embodiment, the inter-element spacing of the electromagnetic
scattering elements includes at least five electromagnetic
scattering elements per the free-space wavelength.
In an embodiment, the plurality of electromagnetic wave scattering
elements 1912 are operable in combination to produce a dynamically
controllable radiation pattern 1919. In an embodiment, the
plurality of electromagnetic wave scattering elements are operable
in combination to produce a variable radiation pattern providing
localization on the possible interfering signal 1997. In an
embodiment, the plurality of electromagnetic wave scattering
elements are operable in combination to produce a controllable
radiation envelope. In an embodiment, the plurality of
electromagnetic wave scattering elements are operable in
combination to produce a controllable radiation pattern in response
to a control signal.
In an embodiment, the gain definition circuit 1930 includes a gain
definition circuit configured to define an antenna radiation
pattern 1919 with a field of view 1916 shaped to facilitate
searching at least a portion of the undesired field of view 1988 of
the associated antenna 1980 for the possible interfering signal
1997. In an embodiment, the gain definition circuit includes a gain
definition circuit configured to define a series of antenna
radiation patterns with fields of view shaped to facilitate
searching at least a portion of the undesired field of view of the
associated antenna for the possible interfering signal. In an
embodiment, the gain definition circuit includes a gain definition
circuit configured to define an antenna radiation pattern with a
field of view shaped to localize at least a portion of the
undesired field of view of the associated antenna for the possible
interfering signal. In an embodiment, the gain definition circuit
is further configured to instruct the antenna controller 1940 to
implement the defined radiation pattern. In an embodiment, the
defined radiation pattern is selected based on trial and error. In
an embodiment, the defined radiation pattern is selected from a
library of potential radiation patterns. In an embodiment, the
defined radiation pattern is selected from a history of radiation
patterns previously established in the surface scattering antenna
1910. In an embodiment, the undesired field of view of the
associated antenna includes a terrestrial or low altitude region.
For example, the undesired field of view may include a field of
view below 20 degrees zenith. For example, the undesired field of
view may include below the earth's horizon. In an embodiment, the
undesired field of view of the associated antenna includes a field
of view away from a source of a target signal. For example, such as
away from one or more orbiting objects, such as the spaceborne
sources 1992 and 1994, or away from a likely direction of a
terrestrial target. In an embodiment, the desired field of view of
the associated antenna includes a skyward or hemispherical view.
For example, a skyward or hemispherical field of view may include a
field of view likely to be occupied by an orbiting object, a
neighboring satellite in an intra-satellite communication system,
or a likely direction of a terrestrial target. In an embodiment,
the desired field of view of the associated antenna includes a
field of view that includes a source of the target signal.
In an embodiment, the antenna controller 1940 is further configured
to implement the defined radiation pattern 1919. In an embodiment,
the antenna controller is configured to establish at least two
radiation patterns in the surface scattering antenna 1910 by
dynamically controlling the respective electromagnetic responses of
the electromagnetic wave scattering elements of the plurality of
electromagnetic wave scattering elements 1912. In an embodiment,
the antenna controller is configured to establish the defined
radiation pattern in the surface scattering antenna by applying a
bias activating the respective electromagnetic response of the
electromagnetic wave scattering elements of the plurality of
electromagnetic wave scattering elements. In an embodiment, the
bias includes a bias voltage, bias field, bias current, or biasing
mechanical inputs.
In an embodiment, the correction circuit 1950 is further configured
to detect the possible interfering signal 1997. In an embodiment,
the associated antenna 1980 includes an associated skyward or
hemispherically sensitive antenna configured to receive
electromagnetic signals transmitted by an airborne or spaceborne
source. For example, an airborne or spaceborne source includes a
source flying or orbing above the horizon 1998 of the earth.
In an embodiment, the possible interfering signal 1997 includes a
possible jamming signal. In an embodiment, the possible interfering
signal includes a possible spoofing signal. In an embodiment, the
possible interfering signal includes a possible malicious signal.
In an embodiment, the possible interfering signal includes a
possible intentionally interfering signal. In an embodiment, the
possible interfering signal includes a possible unintentionally
interfering signal.
In an embodiment, the correction circuit 1950 is configured to
cancel a component of the received possible interfering signal 1996
in the contemporaneously received signal 1993 by the associated
antenna 1980. In an embodiment, the gain definition circuit 1930 is
further configured to maximize a received strength of the possible
interfering signal by establishing the antenna radiation pattern
1919 in response to data received from the correction circuit. In
an embodiment, the correction circuit is configured to subtract the
possible interfering signal from the contemporaneously received
signal by the associated antenna. In an embodiment, the correction
circuit includes a variable attenuator configured to adjust the
signal strength of a received possible interfering signal, and is
configured to subtract or offset the possible interfering signal at
the adjusted strength level from the contemporaneously received
signal by the associated antenna.
In an embodiment, the correction circuit 1950 includes an adaptive
correction circuit. In an embodiment, the adaptive correction
circuit is configured to determine phases and amplitudes of the
received possible interfering signal 1997 and the contemporaneously
received signal 1993. The adaptive correction circuit is further
configured to combine the possible interfering signal and the
contemporaneously received signal to produce a reduction of an
influence of the received possible interfering signal in the
contemporaneously received signal. In an embodiment, the adaptive
correction circuit includes use of space-time adaptive processing
in reducing an influence of the received possible interfering
signal in the contemporaneously received signal. In an embodiment,
the correction circuit includes a correction circuit configured to
using a signal-processing technique to reduce an influence of the
received possible interfering signal in the contemporaneously
received signal. For example, the correction circuit may employ
analog phase shifting and summing at the received frequency. For
example, the correction circuit may employ analog phase shifting
and summing at a baseband or IF frequency. For example, the
correction circuit may employ A/D conversion and digital
combining.
In an embodiment, the gain definition circuit 1930 is further
configured to facilitate detection of the possible interfering
signal 1997 by adaptively varying a radiation pattern 1919 of the
surface scattering antenna 1910 to home in on the possible
interfering signal. For example, the homing in thereby producing a
higher fidelity reception of the possible interfering signal for
use in signal cancellation.
In an embodiment of the system 1905, a peripheral portion of the
associated antenna 1980 includes the surface scattering antenna
1910. In an embodiment, the peripheral portion of the associated
antenna includes an electromagnetic wave deflecting structure
configured to direct an arriving electromagnetic wave into the
defined radiation pattern of the surface scattering antenna. In an
embodiment, the wave deflecting structure includes a wave
reflecting structure. In an embodiment, the wave deflecting
structure includes a lens structure. For example, the lens
structure may include a metamaterial lens structure. In an
embodiment, the wave deflecting structure includes a prism
structure. For example, the prism structure may include a
metamaterial prism structure.
In an embodiment, the system 1905 includes the associated antenna
1980 with the desired field of view 1987. In an embodiment, the
surface scattering antenna 1910 is configured to be mounted on an
airborne vehicle. For example, an airborne vehicle may include a
fixed or rotary winged aircraft. For example, a fixed wing aircraft
may include a drone. In an embodiment, the surface scattering
antenna is configured to be mounted on a missile. For example, a
missile may include a ground-to-ground missile, an air-to-ground
missile, or a ballistic missile. In an embodiment, the surface
scattering antenna is configured to be mounted on a terrestrial
vehicle. In an embodiment, the system includes a space-based
satellite navigation system receiver 1960. For example, the
receiver may include a GPS receiver.
FIG. 22 illustrates an example operational flow 2000. After a start
operation, the operational flow includes a gain characterization
operation 2010. The gain characterization operation includes
defining an antenna radiation pattern configured to receive in a
surface scattering antenna a possible interfering signal
transmitted within an operating frequency band of an associated
antenna. The associated antenna having field of view that includes
a desired field of view and an undesired field of view, and the
surface scattering antenna having a field of view covering at least
a portion of the undesired field of view. In an embodiment, the
gain characterization operation may be implemented using the gain
definition circuit 1930 described in conjunction with FIG. 20. A
beam-forming operation 2020 includes establishing the defined
radiation pattern in the surface scattering antenna by respectively
activating the electromagnetic response of selected electromagnetic
wave scattering elements of the plurality of electromagnetic wave
scattering elements. In an embodiment, the beam-forming operation
may be implemented by the antenna controller 1940 respectively
activating the electromagnetic response of selected electromagnetic
wave scattering elements of the plurality of electromagnetic wave
scattering elements 1912 of the surface scattering antenna 1910
described in conjunction with FIGS. 21-22. A signal acquisition
operation 2030 includes receiving the possible interfering signal
with the defined antenna radiation pattern established in the
surface scattering antenna. For example, the signal acquisition
operation may be implemented by the surface scattering antenna 1910
receiving the possible interfering signal 1997 described in
conjunction with FIG. 19. A signal processing operation 2040
includes reducing an influence of the possible interfering signal
in a contemporaneously received signal by the associated antenna.
In an embodiment, the signal processing operation may be
implemented by the correction circuit 1950 offsetting the possible
interfering signal 1197 from the contemporaneously received signal
1993 by the associated antenna 1980 described in conjunction with
FIGS. 21-22. The operational flow includes an end operation. The
surface scattering antenna includes an electromagnetic waveguide
structure and the plurality of electromagnetic wave scattering
elements distributed along the waveguide structure. The plurality
of waveguides have an inter-element spacing substantially less than
a free-space wavelength of a highest operating frequency of the
surface scattering antenna. Each electromagnetic wave scattering
element of the plurality of electromagnetic wave scattering
elements have a respective activatable electromagnetic response to
a guided wave propagating in the waveguide structure. The plurality
of electromagnetic wave scattering elements are operable in
combination to produce a controllable radiation pattern.
In an embodiment, the operation flow 2000 may include a second
iteration operation. The second iteration operation includes
reshaping the antenna radiation pattern established in the surface
scattering antenna in response to an aspect of the received
possible interfering signal. The second iteration operation
includes receiving another instance of the possible interfering
signal on the operating frequency of the another antenna with the
reshaped antenna radiation pattern established in the surface
scattering antenna. The second iteration operation may include the
signal processing operation 2040 reducing an influence of the
possible interfering signal in a contemporaneously received signal
by the associated antenna based upon the received another instance
of the possible interfering signal.
FIG. 23 illustrates an example system 2100. The example system
includes means 2110 for defining an antenna radiation pattern
configured to receive in a surface scattering antenna a possible
interfering signal transmitted within an operating frequency band
of an associated antenna. The associated antenna having field of
view that includes a desired field of view and an undesired field
of view, and the surface scattering antenna having a field of view
covering at least a portion of the undesired field of view. The
example system includes means 2120 for establishing the defined
radiation pattern in the surface scattering antenna by respectively
activating the electromagnetic response of selected electromagnetic
wave scattering elements of the plurality of electromagnetic wave
scattering elements. The system includes means 2130 for receiving
the possible interfering signal with the defined antenna radiation
pattern established in the surface scattering antenna. The system
includes means 2140 for reducing an influence of the possible
interfering signal in a signal contemporaneously received by the
associated antenna. The surface scattering antenna 2150 includes an
electromagnetic waveguide structure, and the plurality of
electromagnetic wave scattering elements distributed along the
waveguide structure. The electromagnetic wave scattering elements
have an inter-element spacing substantially less than a free-space
wavelength of a highest operating frequency of the surface
scattering antenna. Each electromagnetic wave scattering element of
the plurality of electromagnetic wave scattering elements have a
respective activatable electromagnetic response to a guided wave
propagating in the waveguide structure, the plurality of
electromagnetic wave scattering elements operable in combination to
produce a controllable radiation pattern.
FIG. 24 illustrates an environment 2300 in which embodiments may be
implemented. The environment includes the horizon 1998, at least
two spaceborne sources transmitting a target signal, illustrated by
the spaceborne sources 1992 and 1994 respectively transmitting the
target signals 1993 and 1995. The environment includes a
terrestrial source transmitting the possible interfering signal,
illustrated by the vehicle 1996 transmitting the possible
interfering signal 1997. The environment includes an antenna system
2305.
The antenna system 2305 includes an antenna assembly 2310 and
components 2350. The antenna assembly includes at least two surface
scattering antenna segments, which are illustrated as the surface
scattering antenna segments 2320A-2320D. Each segment of the at
least two surface scattering antenna segments includes a respective
electromagnetic waveguide structure, which are illustrated as
waveguide structures 2328A-2328D, and a respective plurality of
electromagnetic wave scattering elements, which are illustrated as
a plurality of electromagnetic wave scattering elements
2320A-2320D. The plurality of electromagnetic wave scattering
elements are distributed along the waveguide structure and have an
inter-element spacing substantially less than a free-space
wavelength of a highest operating frequency of the antenna segment.
Each electromagnetic wave scattering element of the plurality of
electromagnetic wave scattering elements has a respective
activatable electromagnetic response to a guided wave propagating
in their respective waveguide structure. The plurality of
electromagnetic wave scattering elements of each antenna segment
are operable in combination to produce a controllable radiation
pattern, which are illustrated as respective radiation patterns
2329A-2329D. Furthermore, the at least two surface scattering
antennas are operable in combination to produce a controllable
radiation pattern. In an embodiment, the at least two surface
scattering antenna segments include at least two surface scattering
antenna apertures.
FIG. 25 illustrates the components 2350 of the antenna system 2305.
The components 2350 of the antenna system include a gain definition
circuit 2360 configured to define a series of at least two
radiation patterns implementable by the at least two surface
scattering antenna segments. The series of at least two respective
radiation patterns is selected to facilitate a convergence on an
antenna radiation pattern that maximizes a specific reception
performance metric that includes reception of a signal from a
desired field of view or rejection of a signal from an undesired
field of view. In an embodiment, the signal from a desired field of
view includes a desired signal. In an embodiment, the signal from
the undesired field of view includes a possible interfering signal.
The antenna system includes an antenna controller 2370 configured
to sequentially establishing each radiation pattern of the series
of at least two radiation patterns by activating the respective
electromagnetic response of selected electromagnetic wave
scattering elements of the plurality of electromagnetic wave
scattering elements of the at least two surface scattering antenna
segments. The antenna system includes a receiver 2380 configured to
receive signals from the desired field of view and signals from the
undesired field of view.
For example, in operation, the gain definition circuit 2360 and the
antenna controller 2370 are configured to initially look for a
signal from a desired field of view, illustrated as the signal 1193
from the spaceborne source 1992. If in the course of receiving the
signal from the desired field of view, a possible malicious signal
from a low zenith source, illustrated as the signal 1997 from the
possible interfering signal 1996 is also received, the gain
definition circuit 2360 and the antenna controller 2370 iteratively
tune the fringes of the radiation pattern of at least one segment
of the at least two segments 2320A-2320D to see what happens with
the received lower zenith signal. For example, the antenna
controller may see what happens to the fringes on one or two
segments are shifted in a direction by 1/2 wavelength. The antenna
controller looks to see if the combination of the signal strength
of the undesired field of view is reduced or not. The antenna
controller keeps iteratively tuning until an acceptably low or
minimum combination of the signal strength of the undesired field
of view results, and then the receiver 2380 processes the combined
signals.
In an embodiment, the antenna assembly 2310 includes an at least
substantially planar arrangement having the at least two antenna
segments. In an embodiment, the antenna assembly includes a
conformal arrangement of the at least two antenna segments. For
example, the conformal arrangement may be configured to be mounted
on or carried by an exterior surface of an aircraft or missile. In
an embodiment, the antenna assembly includes a first substantially
planar antenna segment physically joined with a second
substantially planar antenna segment. In an embodiment, the
aperture planes may be collinear or non-collinear. In an
embodiment, the antenna assembly includes a first substantially
planar antenna segment physically abutting or contiguous with a
second substantially planar antenna segment. In an embodiment, the
antenna assembly includes a first antenna segment 2320A optimized
in area, orientation, or mounting for scattering to or receiving
signals from a specific set or distribution of objects. For
example, the first antenna segment may be optimized for receiving a
signal transmitted by a space-based satellite navigation system.
For example, a second antenna segment 2320B may be optimized with a
relatively small aperture for a field of view that includes
near-zenith angles. In an embodiment, a first segment of the at
least two segments includes a receiving aperture that is larger
than a receiving aperture of a second segment of the at least two
segments. In an embodiment, the receiving aperture of a first
segment of the at least two segments and a receiving aperture of a
second segment of the at least two segments are substantially
equal.
In an embodiment, the undesired field of view signal includes a
possible interfering signal. In an embodiment, the desired field of
view signal includes a possible target or desired signal. In an
embodiment, the series of at least two radiation patterns is
defined in advance.
In an embodiment, the series of at least two radiation patterns is
defined on the fly. In an embodiment, the series of at least two
radiation patterns is incrementally defined based on trial and
error. In an embodiment, the series of at least two radiation
patterns is incrementally and adaptively defined based on trial and
error. In an embodiment, the series of the at least two radiation
patterns is selected from a library of potential radiation
patterns. In an embodiment, the series of the at least two
radiation patterns is selected randomly from radiation patterns
implementable by the at least two antenna segments. In an
embodiment, the series of at least two radiation patterns is
estimated or projected to facilitate the convergence. In an
embodiment, the radiation performance metric includes optimizing a
combined signal strength received from the desired field of view
and minimizing a combined signal strength from an undesired field
of view. In an embodiment, the radiation performance metric
includes maximizing a combined signal strength received from a
desired field of view and minimizing a combined signal strength
received from a undesired field of view. In an embodiment, the
radiation performance metric includes a weighted combination of one
or more antenna reception performance factors, subject to at least
one constraint. In an embodiment, an antenna reception radiation
performance factor includes an amplitude of the signal received
from the desired field of view, or an amplitude of the signal
received from the undesired field of view. In an embodiment, an
antenna reception radiation performance factor includes antenna
gain for one or more desired directions or angular regions, or
antenna gain for one or more undesired directions or angular
regions. In an embodiment, an antenna reception radiation
performance factor includes signal to noise ratio, signal to
interference ratio, signal to clutter ratio, channel capacity, data
rate, or error rate. In an embodiment, the constraint of the
antenna radiation performance metric includes a constraint on
amplitude of the signal received from the desired field of view, or
on an amplitude of the signal received from the undesired field of
view. In an embodiment, the constraint of the antenna radiation
performance metric includes a constraint on antenna gain for one or
more desired directions or angular regions, or antenna gain for one
or more undesired directions or angular regions. In an embodiment,
the constraint of the antenna radiation performance metric includes
a constraint on signal to noise ratio, signal to interference
ratio, signal to clutter ratio, channel capacity, data rate, or
error rate. In an embodiment, the optimized combined signal
strength received from a desired field of view includes a combined
desired field of view signal optimized for processing by the
receiver circuit.
In an embodiment, the gain definition circuit 2360 includes an
adaptive gain definition circuit configured to define a second
radiation pattern of the at least two radiation patterns responsive
to a combined signal received from a desired field of view and a
combined signal received from a undesired field of view with the at
least two antenna segments configured in a first radiation pattern
of the at least two radiation patterns. In an embodiment, the
series of at least two radiation patterns are defined to adjust an
amplitude or phase of the undesired field of view signal received
by a first antenna segment relative to an amplitude or phase of the
undesired field of view signal received by a second antenna segment
of the at least two segments of the antenna assembly in a manner
predicted to minimize the combined signal received from the
undesired field of view by the first segment and the second
segment. For example, the radiation patterns of the two individual
segments are adjusted for the desired field of view signals to
remain substantially in phase and for the undesired field of view
signals to become substantially out of phase and self-cancelling.
In an embodiment, the adaptive gain definition circuit is
configured to define the second radiation pattern of the series of
at least two radiation patterns by modifying a previously
implemented first radiation pattern of the series of at least two
radiation patterns. In an embodiment, the adaptive gain definition
circuit is configured to define the series of at least two
respective radiation patterns in response to a library of at least
three potential radiation patterns. In an embodiment, the adaptive
gain definition circuit is configured to define the series of at
least two respective radiation patterns in response to a library of
at least three potential radiation patterns and a parameter of the
undesired field of view signal. In an embodiment, the adaptive gain
definition circuit is configured to define the series of at least
two radiation patterns in response to a selection algorithm. In an
embodiment, the adaptive gain definition circuit is configured to
make at least two successive iterations of defining the set of at
least two respective radiation patterns during a course of
facilitating a convergence on an optimized combined signal strength
received from the desired field of view and a minimized combined
signal strength received from the undesired field of view.
In an embodiment, the series of at least two radiation patterns is
defined to: (a) adjust an amplitude or phase of the undesired field
of view signal received by the first antenna segment relative to an
amplitude or phase of the undesired field of view signal received
by the second antenna segment of the at least two segments of the
antenna assembly in a manner predicted to increase a degradation in
the combined signals received from the undesired field of view by
the first segment and the second segment; and (b) adjust an
amplitude or phase of the desired field of view signal received by
a first antenna segment relative to an amplitude or phase of the
desired field of view signal received by a second antenna segment
of the at least two segments of the antenna assembly in a manner
predicted to minimize any degradation in the combined signals
received from the desired field of view by the first segment and
the second segment. For example, in an embodiment, the amplitude or
phase of the desired field of view signal source may be degraded
less than 10% while the amplitude or phase of the undesired field
of view may be degraded by at least about 50%. In an embodiment,
the series of at least two radiation patterns are defined to
respectively adjust an amplitude or phase the desired field of view
and of the undesired field of view signals received by the at least
two segments of the antenna assembly in a manner predicted to
minimize the combined signal received from the undesired field of
view while substantially maintaining the combined signal received
from the desired field of view. In an embodiment, the adaptive gain
definition circuit is configured to define a second radiation
pattern of the series of at least two radiation patterns in
response to an amplitude or phase of a received desired field of
view signal with the antenna segments configured in a first
radiation pattern of the series of at least two radiation patterns.
For example, the adaptive gain definition circuit may be configured
to iteratively define the second radiation pattern. In an
embodiment, the adaptive gain definition circuit is configured to
define a second radiation pattern of the series of at least two
radiation patterns in response to an amplitude or phase of a
received undesired field of view signal with the antenna segments
configured in a first radiation pattern of the series of at least
two radiation patterns. In an embodiment, the adaptive gain
definition circuit is configured to define a second radiation
pattern of the series of at least two radiation patterns in
response to an amplitude or phase of a received desired field of
view signal, and an amplitude or phase of a received undesired
field of view signal, both received with the antenna segments
configured a first radiation pattern of the series of at least two
radiation patterns.
In an embodiment, the at least two surface scattering antenna
segments, for example segments 2320C and 2320D, may be physically
contiguous or non-contiguous. For example, the at least two surface
scattering antenna segments may or may not share driver circuitry.
For example, the at least two surface scattering antenna segments
are only required to be separate RF apertures.
In an embodiment, the antenna assembly 2310 includes at least one
respective electromagnetic waveguide structure for each segment of
the at least two segments. For example, the surface scattering
antenna 2320B includes a waveguide structure 2328B, and the surface
scattering antenna 2320C includes a waveguide structure 2328C. In
an embodiment, the electromagnetic waveguide structure is
configured to generate at least one beam. In an embodiment, the
components 2350 of the antenna system 2305 further includes a
signal processing circuit 2385 configured to combine signals
received from the at least two antenna segments and provide a
cancellation of the signal from the undesired field of view. In an
embodiment, the signal processing circuit is further configured to
combine signals received from two or more antenna segments for
increased gain. In an embodiment, the receiver 2380 includes a
space-based satellite navigation system receiver.
FIG. 26 illustrates an example operational flow 2400. After a start
operation, the operational flow includes a first gain
characterization operation 2410. The first gain characterization
operation includes defining a first-iteration radiation pattern
implementable by a first surface scattering antenna segment and
another first-iteration radiation pattern implementable by a second
surface scattering antenna segment of at least two surface
scattering antenna segments of an antenna assembly. In an
embodiment, the first gain characterization operation may be
implemented using the gain definition circuit 2360 described in
conjunction with FIG. 25. A first beam-forming operation 2420
includes implementing the first-iteration radiation pattern in the
first surface scattering antenna segment and the another
first-iteration radiation pattern in the second surface scattering
antenna segment. The first-iteration radiation patterns are
established by activating respective electromagnetic responses of
selected electromagnetic wave scattering elements of a plurality of
electromagnetic wave scattering elements in each of the first and
the second surface scattering antenna segments. In an embodiment,
the first-beam forming operation may be implemented by the antenna
controller 2370 respectively activating the electromagnetic
response of selected electromagnetic wave scattering elements of
the first and the second surface scattering antenna segments, such
as scattering elements 2322B of surface scattering antenna segment
2320B and scattering elements 2322C of surface scattering segment
2320C, described in conjunction with FIGS. 26 and 27. A first
signal acquisition operation 2430 includes receiving a combined
signal in a desired field of view and a combined signal from an
undesired field of view with the first and second antenna segments
configured in the first-iteration radiation patterns. In an
embodiment, the first signal acquisition operation may be
implemented using the receiver 2380 described in conjunction with
FIG. 25. A second gain characterization operation 2440 includes
defining a second-iteration radiation pattern implementable by the
first surface scattering antenna segment and another
second-iteration radiation pattern implementable by the second
surface scattering antenna segment. The second-iteration patterns
are selected in response to an aspect of the received signal in the
desired field of view or the received signal from the undesired
field of view, and configured to facilitate a convergence on an
antenna radiation pattern that maximizes a specific reception
performance metric. In an embodiment, the second characterization
pattern may be implemented using the gain definition circuit 2360
described in conjunction with FIG. 25. A second beam-forming
operation 2450 includes implementing the second-iteration radiation
pattern in the first surface scattering antenna segment and the
another second-iteration radiation pattern in a second surface
scattering antenna segment. The second-iteration radiation patterns
established by activating respective electromagnetic response of
selected electromagnetic wave scattering elements of a plurality of
electromagnetic wave scattering elements in each of the first and
second surface scattering antenna segments. In an embodiment, the
second-beam forming operation may be implemented by the antenna
controller 2370 respectively activating the electromagnetic
response of selected electromagnetic wave scattering elements of
the first and the second surface scattering antenna segments, such
as scattering elements 2322B of surface scattering antenna segment
2320B and scattering elements 2322C of surface scattering segment
2320C, described in conjunction with FIGS. 26 and 27. A second
signal acquisition operation 2460 includes receiving the combined
signal in a desired field of view and the combined signal from an
undesired field of view with the first and second antenna segments
configured in the second-iteration radiation patterns in accordance
with the maximized performance metric. In an embodiment, the second
signal acquisition operation may be implemented using the receiver
2380 described in conjunction with FIG. 25. A communication
operation 2470 includes outputting the combined signal in a desired
field of view and the combined signal from an undesired field of
view received in accordance with the maximized performance metric.
The operational flow includes an end operation. The antenna
assembly includes at least two surface scattering antenna segments.
Each segment of the at least two surface scattering antenna
segments includes a respective electromagnetic waveguide structure,
and a respective a plurality of electromagnetic wave scattering
elements. The plurality of electromagnetic wave scattering elements
are distributed along the waveguide structure and have an
inter-element spacing substantially less than a free-space
wavelength of a highest operating frequency of the antenna segment.
Each electromagnetic wave scattering element of the plurality of
electromagnetic wave scattering elements has a respective
activatable electromagnetic response to a guided wave propagating
in their respective waveguide structure, and the plurality of
electromagnetic wave scattering elements operable in combination to
produce a controllable radiation pattern.
In an embodiment, a radiation pattern includes a far field response
pattern. For example, a far field response pattern may include a
gain response or a phase response. In an embodiment of the first
gain characterization operation 2410, the first-iteration radiation
pattern and the another first-iteration radiation pattern have an
at least substantially similar far field response pattern. In an
embodiment of the first gain characterization operation, the
first-iteration radiation pattern and the another first-iteration
radiation pattern have a substantially dissimilar far field
response pattern. For example, a substantially dissimilar far field
response pattern may include greater than a 20 dB gain difference
at a point in the far field response pattern, or greater than a 10
degree phase shift.
In an embodiment of the second gain characterization operation
2440, the second-iteration radiation pattern and the
first-iteration radiation pattern have a substantially similar far
field response pattern. In an embodiment of the second gain
characterization operation, the first-iteration radiation pattern
and the second-iteration radiation pattern have a substantially
dissimilar far field response pattern. In an embodiment of the
second gain characterization operation, the second-iteration
radiation pattern and the another second-iteration radiation
pattern have a substantially dissimilar far field response pattern.
For example, a substantially dissimilar far field response pattern
may include greater than a 20 dB gain difference at a point in the
far field response pattern, or greater than a 10 degree phase
shift. In an embodiment of the second gain characterization
operation, the aspect of the received desired field of view signal
and the undesired field of view signal includes a direction of the
desired field of view signal and a direction the undesired field of
view signal relative to a plane formed by the first surface
scattering antenna or the second surface scattering antenna. In an
embodiment of the second gain characterization operation, the
aspect of the received desired field of view signal and the
undesired field of view signal includes a phase of the desired
field of view signal or a phase the undesired field of view
signal.
FIG. 27 illustrates an example system 2500. The system includes
means 2510 for defining a first-iteration radiation pattern
implementable by a first surface scattering antenna segment and
another first-iteration radiation pattern implementable by a second
surface scattering antenna segment of the at least two surface
scattering antenna segments of an antenna assembly. The system
includes means 2520 for implementing the first-iteration radiation
pattern in the first surface scattering antenna segment and the
another first-iteration radiation pattern in the second surface
scattering antenna segment. The first-iteration radiation patterns
established by activating respective electromagnetic response of
selected electromagnetic wave scattering elements of a plurality of
electromagnetic wave scattering elements in each of the first and
the second surface scattering antenna segments. The system includes
means 2530 for receiving a combined signal from a desired field of
view and a combined signal from an undesired field of view with the
first and second antenna segments configured in the first-iteration
radiation patterns. The system includes means 2540 for defining a
second-iteration radiation pattern implementable by the first
surface scattering antenna segment and another second-iteration
radiation pattern implementable by the second surface scattering
antenna segment. The second-iteration patterns are selected in
response to an aspect of the received signal from the desired field
of view or the received signal from the undesired field of view,
and configured to facilitate a convergence on an antenna radiation
pattern that maximizes a specific reception performance metric. The
system includes means 2550 for implementing the second-iteration
radiation pattern in the first surface scattering antenna segment
and the another second-iteration radiation pattern in a second
surface scattering antenna segment. The second-iteration radiation
patterns established by activating respective electromagnetic
response of selected electromagnetic wave scattering elements of a
plurality of electromagnetic wave scattering elements in each of
the first and second surface scattering antenna segments. The
system includes means 2560 for receiving the combined signal from a
desired field of view and the combined signal from an undesired
field of view with the first and second antenna segments configured
in the second-iteration radiation patterns in accordance with the
maximized performance metric. The system includes means 2570 for
outputting the combined signal from a desired field of view and the
combined signal from an undesired field of view received in
accordance with the maximized performance metric.
The antenna assembly 2580 includes at least two surface scattering
antenna segments. Each segment of the at least two surface
scattering antenna segments respectively includes an
electromagnetic waveguide structure and a plurality of
electromagnetic wave scattering elements. The plurality of
electromagnetic wave scattering elements distributed along the
waveguide structure and having an inter-element spacing
substantially less than a free-space wavelength of a highest
operating frequency of the antenna segment. Each electromagnetic
wave scattering element of the plurality of electromagnetic wave
scattering elements has a respective activatable electromagnetic
response to a guided wave propagating in their respective waveguide
structure, the plurality of electromagnetic wave scattering
elements operable in combination to produce a controllable
radiation pattern.
The foregoing detailed description has set forth various
embodiments of the devices and/or processes via the use of block
diagrams, flowcharts, and/or examples. Insofar as such block
diagrams, flowcharts, and/or examples contain one or more functions
and/or operations, it will be understood by those within the art
that each function and/or operation within such block diagrams,
flowcharts, or examples can be implemented, individually and/or
collectively, by a wide range of hardware, software, firmware, or
virtually any combination thereof.
All references cited herein are hereby incorporated by reference in
their entirety or to the extent their subject matter is not
otherwise inconsistent herewith.
In some embodiments, "configured" includes at least one of
designed, set up, shaped, implemented, constructed, or adapted for
at least one of a particular purpose, application, or function.
It will be understood that, in general, terms used herein, and
especially in the appended claims, are generally intended as "open"
terms. For example, the term "including" should be interpreted as
"including but not limited to." For example, the term "having"
should be interpreted as "having at least." For example, the term
"has" should be interpreted as "having at least." For example, the
term "includes" should be interpreted as "includes but is not
limited to," etc. It will be further understood that if a specific
number of an introduced claim recitation is intended, such an
intent will be explicitly recited in the claim, and in the absence
of such recitation no such intent is present. For example, as an
aid to understanding, the following appended claims may contain
usage of introductory phrases such as "at least one" or "one or
more" to introduce claim recitations. However, the use of such
phrases should not be construed to imply that the introduction of a
claim recitation by the indefinite articles "a" or "an" limits any
particular claim containing such introduced claim recitation to
inventions containing only one such recitation, even when the same
claim includes the introductory phrases "one or more" or "at least
one" and indefinite articles such as "a" or "an" (e.g., "a
receiver" should typically be interpreted to mean "at least one
receiver"); the same holds true for the use of definite articles
used to introduce claim recitations. In addition, even if a
specific number of an introduced claim recitation is explicitly
recited, it will be recognized that such recitation should
typically be interpreted to mean at least the recited number (e.g.,
the bare recitation of "at least two chambers," or "a plurality of
chambers," without other modifiers, typically means at least two
chambers).
In those instances where a phrase such as "at least one of A, B,
and C," "at least one of A, B, or C," or "an [item] selected from
the group consisting of A, B, and C," is used, in general such a
construction is intended to be disjunctive (e.g., any of these
phrases would include but not be limited to systems that have A
alone, B alone, C alone, A and B together, A and C together, B and
C together, or A, B, and C together, and may further include more
than one of A, B, or C, such as A.sub.1, A.sub.2, and C together,
A, B.sub.1, B.sub.2, C.sub.1, and C.sub.2 together, or B.sub.1 and
B.sub.2 together). It will be further understood that virtually any
disjunctive word or phrase presenting two or more alternative
terms, whether in the description, claims, or drawings, should be
understood to contemplate the possibilities of including one of the
terms, either of the terms, or both terms. For example, the phrase
"A or B" will be understood to include the possibilities of "A" or
"B" or "A and B."
The herein described aspects depict different components contained
within, or connected with, different other components. It is to be
understood that such depicted architectures are merely examples,
and that in fact many other architectures can be implemented which
achieve the same functionality. In a conceptual sense, any
arrangement of components to achieve the same functionality is
effectively "associated" such that the desired functionality is
achieved. Hence, any two components herein combined to achieve a
particular functionality can be seen as "associated with" each
other such that the desired functionality is achieved, irrespective
of architectures or intermedial components. Likewise, any two
components so associated can also be viewed as being "operably
connected," or "operably coupled," to each other to achieve the
desired functionality. Any two components capable of being so
associated can also be viewed as being "operably couplable" to each
other to achieve the desired functionality. Specific examples of
operably couplable include but are not limited to physically
mateable or physically interacting components or wirelessly
interactable or wirelessly interacting components.
With respect to the appended claims the recited operations therein
may generally be performed in any order. Also, although various
operational flows are presented in a sequence(s), it should be
understood that the various operations may be performed in other
orders than those which are illustrated, or may be performed
concurrently. Examples of such alternate orderings may include
overlapping, interleaved, interrupted, reordered, incremental,
preparatory, supplemental, simultaneous, reverse, or other variant
orderings, unless context dictates otherwise. Use of "Start,"
"End," "Stop," or the like blocks in the block diagrams is not
intended to indicate a limitation on the beginning or end of any
operations or functions in the diagram. Such flowcharts or diagrams
may be incorporated into other flowcharts or diagrams where
additional functions are performed before or after the functions
shown in the diagrams of this application. Furthermore, terms like
"responsive to," "related to," or other past-tense adjectives are
generally not intended to exclude such variants, unless context
dictates otherwise.
While various aspects and embodiments have been disclosed herein,
other aspects and embodiments will be apparent to those skilled in
the art. The various aspects and embodiments disclosed herein are
for purposes of illustration and are not intended to be limiting,
with the true scope and spirit being indicated by the following
claims.
* * * * *
References